Why Your Drain Smells Like Sewage

Why it matters in Toronto homes

Every drain in your house has a trap, a curved section that keeps a little water sitting in it as a seal against sewer gas. Vents in the roof keep that water in place. In older Toronto homes, many traps sit in rarely used places such as basement floor drains, old laundry tubs or a second-floor guest shower. Others were built without proper venting during a renovation decades ago. When a trap dries out or is siphoned, sewer gas comes straight in. Persistent odours can also signal a cracked cast-iron pipe or a failed seal under a toilet.

Step-by-step what to do

1. Find the source. Sniff near each drain. A smell strongest in the basement often comes from the floor drain.
2. Refill dry traps by pouring a litre or two of water into unused drains. Adding a spoon of vegetable oil slows evaporation.
3. Clean the sink overflow and pop-up, where hair and soap rot.
4. Check toilets for rocking or water at the base, both signs of a failed wax seal.
5. Run the washing machine empty on a hot cycle with a cleaner if the smell comes from the washer.

Mistakes to avoid

• Masking the smell with air fresheners or drain deodorizers. The gas is still coming in.
• Pouring bleach down a floor drain repeatedly. It does little for a dry trap and can harm old pipe.
• Ignoring a smell that comes and goes with wind or rain. That can point to vent problems.
• Sealing a floor drain shut. It is there to protect your basement from water.

Time to bring in a plumber

Phone us if the smell persists after you have refilled traps and cleaned the drains, if you notice gurgling, or if a toilet seal needs replacing. A plumber can smoke-test the system to find cracked pipes or open connections, check venting, and look for problems in the main line. Odours paired with slow drains in the basement can point to a blockage best handled by floor drain repair or a camera check. Persistent bathroom odours are often solved during a bathroom plumbing renovation, when venting can be corrected properly. If the gurgling started after heavy rain, our guide to sump pump maintenance is also worth reading.

Seasonal smells

Some odours appear only at certain times of year. In winter, a frozen or frost-capped roof vent can stop drains venting properly, causing traps to siphon. In summer, long vacations let traps dry out. If you are leaving the house for a while, pour water into every drain on your return, and in very cold spells watch for gurgling that suggests a blocked vent. Pairing the water with a little cooking oil on top slows evaporation if you leave often.

Common questions