Guide: odours
Smelly Drains and Sewer Gas: Finding the Source
Sewer odour indoors is more than a nuisance; it can point to a fault in the pipes. Here is how to track down the source.
- Biofilm in drains. Sinks and showers build up a smelly film.
- Failed wax ring. A toilet seal that has failed can leak gas.
- Vent problems. Blocked or missing vents let traps siphon dry.
- Cracked pipe. A damaged drain or stack can leak gas into walls.
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Common causes
- Dry traps. Floor drains and rarely used fixtures lose water in their traps, letting sewer gas in.
- Biofilm in drains. Sinks and showers build up a smelly film.
- Failed wax ring. A toilet seal that has failed can leak gas.
- Vent problems. Blocked or missing vents let traps siphon dry.
- Cracked pipe. A damaged drain or stack can leak gas into walls.
What to try first
- Pour water into floor drains and unused fixtures.
- Clean sink and shower drains with hot water and a brush.
- Check that toilets are solid and not rocking.
- Clean the overflow holes in sinks and tubs.
A spoonful of mineral oil floated in the floor drain trap slows evaporation, helping it stay sealed longer.
Time to phone us
Ring us if the smell persists, if it is strongest near a wall or ceiling, or if you notice gurgling when fixtures drain. A camera inspection or smoke test can find hidden leaks. See drain cleaning, sewer camera inspection and toilet repair.
Questions we get about this
Is sewer gas dangerous?
In the small amounts that escape a dry trap, it is mostly unpleasant. Strong or persistent smells should still be traced and fixed without delay.
The odour appears some days and not others. What does that mean?
Traps dry out slowly, wind changes vent pressure, and warm weather makes odours stronger. A pattern like that still points to a fixable cause.