Dry floor drain trap
- Each floor drain has a trap whose water plug keeps sewer gas down. Leave the drain unused long enough and that plug evaporates and gas comes up. Pour a bucket of water into the drain, and a little mineral oil on top to slow evaporation.
- Basement showers and laundry tubs that are seldom used can dry out the same way.
Cleanout cap
- The main cleanout on the street side of the basement has a cap that should be tight with an intact seal. A missing or loose cap lets gas out. Tightening or replacing the cap fixes it.
- Check after any drain cleaning; caps are sometimes not put back properly.
Quick checklist
- Refill drains
- Check cleanout
- Toilet base
- Stack
- Vent
Toilet wax ring
- A basement toilet with a failed wax ring lets gas escape around the base. You may also see water stains or a rocking bowl. Resetting the toilet on a new ring solves it.
- Upstairs toilets can do the same and the smell can travel.
Cracked stack or vent
- Old cast iron stacks can crack, especially near the base. A crack lets gas out even if no water leaks. Vents blocked by debris or ice can also cause traps to siphon dry.
- A plumber can check the stack and vents with a smoke test if the source is not obvious.
Richmond Hill note: most houses here sit on York Region municipal water with fairly hard supply, and many basements have a floor drain tied to the sanitary lateral. Mention both on the phone; it changes what goes on the truck.
Want a second opinion on your own pipes first? Dial (365) 363-1575; the person answering holds the wrench.