Why does my drain smell like sewage?
By the Drain Guru team · Updated September 27, 2026
Quick answer
The most common cause is a dry P-trap: the water seal that blocks sewer gas has evaporated, usually in a rarely-used drain. Run water for a minute to refill it. Other causes are gunk in the sink overflow, a partial clog, a blocked vent, or a damaged pipe. If the smell is strong and spreads through the house, call a plumber.
Five causes
- Dry trap in a guest bath or floor drain: run water, or pour a gallon into the floor drain.
- Biofilm in the sink overflow: scrub it with a bottle brush and hot soapy water.
- Partial clog of hair and gunk that's rotting: clear it.
- Blocked vent: drains gurgle as well as smell.
- Broken or loose pipe or wax seal under a toilet: a constant smell near the toilet base.
A rotten-egg smell can also be a natural gas leak. If you're unsure or it's strong, leave the house and call your gas company from outside.
More questions
Why does my shower drain smell only sometimes?
Often it's biofilm and hair in the drain warming up when hot water runs. Pull the hair out and clean under the cover.
Related answers
General information only. Plumbing codes, prices and landlord-tenant laws vary by location. For gas, electrical, sewer-line or structural problems, contact a licensed professional.