Start with the traps
Each drain has a U-bend whose standing water seals out sewer gas. Floor drains, unused showers and laundry tubs can dry out, especially in summer or in a basement nobody uses often.
Common causes
- Dried-out floor drain trap
- A loose cleanout cap on the main drain
- A cracked cast iron stack or failed joint
- A wax seal leaking under a basement toilet
- A blocked or disconnected vent pipe
Quick fix: Pour a bucket of water into each floor drain and unused shower. Many smells disappear in an hour.
Checks you can make
- Top up every trap with water.
- Look for a loose cleanout plug near the floor drain.
- Sniff around the base of the basement toilet.
- Check for damp patches or rust on the main stack.
When it is something more
If the smell persists, a cracked pipe or vent problem may be the cause. A smoke test or camera inspection can find it.
Safety
Sewer gas in high amounts is unhealthy. If the smell is strong, ventilate the area and call.