Most frequent causes
- Dry floor drain trap
- Rarely used basement shower or sink
- Loose cleanout cap
- Failed toilet wax ring
- Cracked cast iron
- Blocked or disconnected vent
What to try first
- Pour water into each floor drain and unused fixture.
- Check the cleanout caps are tight.
- Look and smell around the base of toilets.
When to call
If the smell persists, we can run a smoke test to find leaks. Persistent smells can also signal a blocked main.
How a smoke test works
We seal the house drains, then pump harmless smoke into the plumbing through a cleanout or vent. Smoke escaping from a cracked pipe, a loose fitting or a dry trap shows exactly where sewer gas is leaking. It is a quick way to find faults behind walls or floors.
Before the test, we let you know so nobody mistakes the smoke for a fire.
Another frequent source is a toilet that was pulled for flooring work and reset on the old wax. The seal looks fine from above but leaks gas at the flange every flush. Rocking the bowl gently with your knee can reveal movement; if it shifts, a reset on a new seal is due.
Related
See floor drain clearing, toilet repair and main sewer line clearing.
Keep-handy checklist
- Keep fat in a tin, not down the kitchen sink
- Check the toilet for a silent leak with a few drops of food colouring
- Note where the main cleanout cap is and keep boxes off it
- Turn the main shut-off a quarter each way once a year so it never seizes
Your questions, answered plainly
Why does the smell come and go?
Weather, wind and usage affect venting and trap levels.