Drain Smells Like Sewage: Who Should You Call?
Urgency: UrgentUpdated 2026-08-31
Short answer
Sewer gas indoors means a trap somewhere is dry, blocked or unvented. Pour two litres of water into every unused floor drain and rarely-used fixture, then wait a day. If the smell persists, call a licensed plumber — the likely causes are a failed vent stack, a dried or broken trap under a floor drain, or a compromised toilet seal.
Who to call: A licensed plumber if refilling traps and cleaning don't clear it.
What to do right now
- 1Pour water down every floor drain, laundry tub and guest bathroom fixture.
- 2Check that the toilet is not rocking — a broken wax seal lets gas past.
- 3Look for a dried trap primer on basement floor drains.
- 4Ventilate the space; sewer gas is unpleasant and, at high concentration, unsafe.
Most likely causes
- Dry P-trap
- Any drain unused for weeks evaporates its water seal and lets gas straight in.
- Failed toilet wax ring
- Usually accompanied by a slight rocking motion in the toilet.
- Blocked or frozen vent stack
- The roof vent gets blocked by a nest or frost, siphoning traps dry as fixtures drain.
- Biofilm build-up
- Rotting organic film in a kitchen or laundry drain smells foul without gas ingress.
What it typically costs in the GTA
$150–$300 for a plumber to diagnose and reseal a trap. $200–$450 to reset a toilet with a new wax ring. $300–$800 to clear a blocked vent stack.
Ranges are typical market pricing for the Greater Toronto Area and vary with access, age of the home, and time of year. Always get the scope in writing before work starts.
Is sewer gas dangerous?
In household concentrations it is mostly a nuisance, but it contains hydrogen sulphide and methane. A persistent, strong smell should not be lived with — it means an open path between the sewer and your air.
Kitchen smells are usually different
A sour smell at the kitchen sink is typically biofilm in the drain or a dirty garburator, not sewer gas. Hot water with baking soda and vinegar, or an enzyme cleaner, usually clears it.
Get the right pro on it
Describe the problem in your own words. We’ll work out which trade you need and connect you with suitable local pros. Free, no obligation.
Frequently asked questions
- Why does the smell come and go?
- Wind and pressure changes push gas back through a compromised trap or vent, so it often appears on windy days or when the furnace runs.
- Can I pour bleach down the drain?
- It masks the symptom briefly and damages some seals. Identify the source instead.
- Should I be worried about a smell only in the basement?
- Basement floor drains are the most common dry trap. Refill it first — that solves it a large share of the time.