A drain smells like sewage or rotten eggs

A sewer smell is unpleasant and a little alarming, but the most common cause is the easiest fix there is: a drain that hasn't been used in a while has simply lost the water in its trap. Often you fix it by running the tap for a minute.

tuneWhat are you noticing?

Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.

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In Canadian homes, start with the simplest cause: a dried-out trap. If the smell comes from a floor drain or a sink, tub, or laundry basin you rarely use, the water seal in its P-trap has probably evaporated. Run the tap (or pour a couple of litres of water down a floor drain) for a minute and see if the smell clears within an hour. Free, and the most common fix by far.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order

Beginner-friendly Doable, with care Safety-critical Call a pro

visibilityHow to check

Identify the smelly drain and ask when it was last used. Floor drains, basement sinks, laundry tubs, guest bathrooms, and seasonal-property fixtures are the classic dry-trap culprits.
Run the tap into that fixture for about a minute — or, for a floor drain, pour a couple of litres of water slowly down it — to refill the U-shaped trap below.
Wait an hour and smell again near the drain. If the sewer smell is gone or fading, a dry trap was the cause; if it's unchanged, move on to biofilm, venting, or a nearby toilet.

buildNo tools schedule5 min

handymanHow to fix it

Refill the water seal by running the fixture for a minute (or pouring a couple of litres down a floor drain). For a floor drain that keeps drying out, add a small splash of mineral oil on top of the water to slow evaporation, and use it — or refill it — regularly.

Run the tap into the smelly fixture for about a minute so water flows through and settles into the U-shaped trap below. For a floor drain with no tap, slowly pour two to four litres of water into it.
For a floor drain or fixture that dries out repeatedly, pour a small splash (a tablespoon or two) of mineral oil down after the water — it floats on top of the seal and slows evaporation.
Set a reminder to run water through rarely-used drains every few weeks, especially over dry winter months and before leaving a property empty.

schedule5 min savings$0–5

gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Refilling a trap by running water is routine homeowner maintenance in every province.

handymanHow to fix it

warning Use an enzyme cleaner, not caustic drain cleanerCaustic (lye or acid) drain cleaners don't digest biofilm well and leave a dangerous slug of chemical sitting in the trap for whoever opens or plunges the drain next — a splash-and-burn risk. Use an enzyme or bacterial treatment instead, wear gloves, and never mix drain products. If you've already poured a chemical cleaner down, flush it well with water before doing any hands-in work.

Remove and clean the stopper, scrub the reachable drain walls and the overflow opening, flush with hot water, and follow up with an enzyme or bacterial drain treatment (not caustic chemical drain cleaner) to digest the biofilm.

Remove the pop-up stopper or drain cover and wipe off the mat of hair, grease, and slime clinging to it and to the reachable drain walls.
Clean the overflow: wrap a bottle brush or a rag on a wire in a rag, run it into the overflow opening near the top of the sink or tub, and scrub — this hidden spot is a common smell source people miss.
Flush with a kettle of hot (not boiling, to protect plastic traps) water, then pour in an enzyme or bacterial drain treatment per its label and leave it to work overnight. Repeat weekly if the smell was strong.

schedule30 min savings$10–25

gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Cleaning a drain and overflow and using an enzyme treatment is permitted homeowner maintenance across Canada. Note: any repair to the vent stack or a buried drain/sewer line is licensed plumbing work — route those causes to a plumber.

visibilityHow to check

Stand over the toilet and gently shift your weight side to side. A toilet that rocks or moves on the floor has likely broken or compressed its wax seal.
Look and smell right at the base where the toilet meets the floor — discoloured or lifting flooring, or the smell being strongest there, both point to a failed seal.
If it rocks or smells at the base, the wax ring needs replacing. Re-seating a toilet is doable for some homeowners, but it means lifting the toilet — many hand this to a plumber.

buildNo tools schedule10 min

warning Replacing a wax ring means lifting the toiletFixing a failed toilet seal means shutting off the water, draining and lifting the toilet off its flange, and re-seating it squarely on a new wax ring — do it crooked and the leak comes back. It's a doable job with care, but it's heavy and awkward, and a damaged flange turns it into a bigger repair. If that's more than you want to take on, it's a quick job for a plumber. (See also the toilet-base-leak page for the water side of this.)

warning Vent clearing usually means the roof — route it upConfirming a vent problem is free from inside (gurgling and smell at several fixtures). Clearing the vent, though, usually means getting onto the roof and working at the vent opening — a fall risk, and worse in ice or snow. In a cold snap the cap can be frost, which returns until the venting is corrected. This is a good job to hand to a plumber rather than climb for.

verifiedWhy this one goes to a pro

A cracked or disconnected drain/sewer line under a floor or in a crawlspace can't be found or fixed at the fixture — it takes a camera inspection and often opening the floor or ground. It also means sewer gas is escaping into the house, which carries methane and hydrogen sulphide, so ventilate the space and don't live with a persistent smell. Have a licensed plumber diagnose and repair it.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

sort

Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.