Common House Smells (And What They Each Mean)

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Tar or Strong Campfire Smell: Creosote in the Chimney

A heavy, resinous, smoky smell that lingers around a fireplace or wood stove — especially one that intensifies when the damper is open — usually points to creosote buildup in the flue. Creosote is the tarry residue that forms when wood smoke cools and condenses inside a chimney, and a thick layer is both a draft problem and a fire hazard. Our primer on 15 carbon monoxide safety facts every Canadian homeowner should know covers the broader safety picture around combustion appliances.

If you notice that smell, stop using the fireplace until you have had it inspected and swept. Look for a WETT-certified (Wood Energy Technology Transfer) chimney sweep — the Canadian standard for wood-burning appliance inspection. Most homeowners who burn wood regularly should schedule a WETT inspection annually at the start of the heating season.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Cat-Urine Smell Without a Cat: Dry Rot or Advanced Mould

A sharp, ammonia-like smell concentrated in one corner of a room, with no cat in the house, is one of the more alarming moisture-related odours. It can indicate advanced mould growth, a dry-rot fungus (Serpula lacrymans) attacking structural wood, or occasionally rodent urine that has saturated an enclosed space.

Because dry rot and advanced mould can indicate serious structural or envelope issues, this is not a DIY diagnostic. Call a home inspector, mould remediation specialist, or structural engineer — whoever your local market has available.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.

Plumbing smells are the ones most homeowners misfile as "just the drain." Sometimes that is accurate — a quick clean solves it. Other times, a persistent plumbing smell is the first sign that something structural in your waste or venting system needs attention.

Sewer Gas Indoors: The Dry P-Trap

Every drain in your home has a P-trap — the curved section of pipe under the sink, behind the toilet, or beneath the tub — that holds a small reservoir of water. That water is the only barrier between your living space and the sewer gas rising up the waste stack. When a trap dries out (because a guest bathroom hasn't been used in weeks, because a floor drain in the basement has evaporated over summer, because you just got back from a long winter away), sewer gas flows freely into the room.

The signature smell is rotten-eggs-from-a-drain — similar to natural gas, but tied to a specific fixture rather than pervasive through the house. The fix is often as simple as running water in every drain for 30 to 60 seconds to refill the trap. Pour a cup of water into rarely-used floor drains. If the smell persists after all traps are refilled, the problem is likely further up the system — a blocked plumbing vent stack, a cracked drain line, or a failed wax ring under a toilet — and that is the point at which you call a licensed plumber.

Rotten Eggs From Hot Water Only: The Water Heater

If the sulphur smell appears only when you run hot water — especially after a vacation or a period of low use — the culprit is almost certainly inside your water heater. Sulphate-reducing bacteria (harmless, but odour-producing) thrive in heated, stagnant water and react with the magnesium anode rod inside the tank to produce hydrogen sulphide gas, which smells exactly like rotten eggs.

The standard fix is a thorough tank flush followed by either an aluminum or zinc-aluminum anode rod replacement, which eliminates the chemistry that creates the smell. This is a worthwhile job to have a plumber handle if you are not comfortable draining and servicing the tank yourself. If your water heater is getting on in years, the bigger decision — repair, replace, rent, or own — is worth stepping back to think through. Our water heater rent-vs-own decision guide walks through the economics.

Sour or Rancid From the Kitchen Sink: Drain Biofilm

A funky, sour, slightly rancid smell that rises from the kitchen sink — especially when the tap is running or the garburator is operating — is usually biofilm buildup on the inside of the drain, the disposal flywheel, and the bottom of the P-trap. Food particles, grease, and organic matter accumulate, bacteria colonize the surface, and the result is an odour that no amount of running water can quite rinse away.

The DIY fix is effective and inexpensive. Clean the garburator splash guard and the underside of the blades, flush the drain with a kettle of boiling water followed by a half-cup of baking soda and a cup of white vinegar, let it sit for 15 minutes, and flush again with hot water. Repeat monthly for a chronic problem. If the smell persists after a thorough cleaning, it may indicate a partial clog or a failing gasket deeper in the line — call a plumber before it escalates.