Drain care
Why Does My Drain Smell Like Sewage, and How Do I Fix It?
A sewage smell from a drain almost always means the trap underneath it has dried out or a vent is blocked — both are simple fixes most homeowners can try before calling a plumber.
A sewage smell coming from a drain almost always means the water seal in the trap underneath it has dried out, letting sewer gas drift back up into your home — or, less often, that a vent pipe on the roof is blocked and gases that should escape outside are being pushed back through your fixtures instead. Both causes are common and usually fixable without tearing anything apart.
Why does a dry trap cause a sewer smell?
Every drain — sink, tub, floor drain, even the one behind your washing machine — has a curved section of pipe called a trap that holds a small amount of water at all times. That standing water is what blocks sewer gas from rising back up through the pipe into your home. If a drain goes unused for a while, like a guest bathroom, a basement floor drain, or a laundry sink you only use occasionally, that water can evaporate. Once the trap runs dry, there's nothing stopping the smell from coming straight up. Running water down the drain for a minute usually refills the trap and the smell disappears within a day.
Could it be a blocked vent instead of a dry trap?
Yes, and this one's less obvious. Your plumbing has vent pipes that run up through the roof to let sewer gas escape outside and let air into the system so water drains smoothly. If a vent gets blocked — often by leaves, a bird's nest, or ice in winter — gas that should be venting outside instead gets pushed back through your drains, and you may also notice gurgling sounds or slow draining along with the smell. This is more common in older Toronto homes with vent stacks that haven't been checked in years, and it's not something you can fix by pouring anything down a drain, since the blockage is on the roof end of the pipe.
Does the smell mean I have a hidden leak, not just a dry trap?
It can. If the smell is strong and persistent rather than coming and going, and especially if it's paired with damp patches, mould, or a musty smell near a wall or under a sink, a cracked or disconnected drain pipe could be leaking sewage gas — and sometimes water — into a wall cavity or under the floor. This is more likely in older housing stock across the city, where original cast iron drain lines have had decades to corrode. A quick camera inspection of the line can usually confirm whether that's what's going on, which GetFixHero offers as main line snaking with camera for $300–500.
What can I try myself before calling a plumber?
Start with the easy stuff. Run water in any drain you don't use often — including floor drains and the overflow drain in a bathtub — for about a minute to refill the trap. Pour a cup of water down the overflow hole in bathroom sinks too, since that has its own small trap that dries out just like the main one. If you have a dishwasher, run a cycle, since its drain line ties into your kitchen plumbing and can develop its own smell from trapped food residue. If the smell comes back within a day or two even after refilling the trap, that points toward a vent blockage or a leak rather than simple evaporation.
When should I call a plumber about a sewer smell?
Call a plumber if refilling the traps doesn't fix it, if the smell is coming from more than one drain at once, if you notice gurgling or slow drains along with the odour, or if there's any sign of dampness or mould near the affected area. A persistent sewer smell that isn't a dry trap usually points to something in the line itself, and drain clearing with GetFixHero typically runs $125–250 if a clog or partial blockage turns out to be the cause.
Frequently asked questions
Is sewer gas actually dangerous to breathe? In small amounts from an occasional dry trap it's mostly just unpleasant, but a strong or ongoing smell is worth taking seriously and having checked, since it means gas is entering your living space in a way your plumbing wasn't designed to allow.
Why does the smell only show up in summer? Warmer weather speeds up evaporation from trap water and also dries out the P-traps in floor drains faster, which is why rarely-used basement and laundry drains tend to start smelling more in summer than in winter.
Can a smell from just one sink mean something different than a whole-house smell? Yes — a smell isolated to one fixture usually points to that fixture's own trap or a nearby vent issue, while a smell noticeable throughout the house is more likely tied to the main vent stack or a larger blockage further down the line, and it's worth mentioning that distinction to your plumber.
A sewer smell is usually a quick fix, but it's worth sorting out before it points to something bigger — request a plumber or message us on Facebook. Free for homeowners, care of GetFixHero.
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