Sewer smell in your bathroom: find the source in 10 minutes

What to do, in order

1. Run water in every fixture for 30 seconds — unused drains (guest bath, floor drain) let traps dry out and pipe sewer gas straight in.
2. Grip the toilet bowl and gently rock: any movement means a failed wax ring letting gas escape — $150–$300 reset.
3. Sniff the sink overflow hole: gunked biofilm there smells exactly like sewer. Flush it with hot water and dish soap via a small funnel.
4. Check for a cleanout plug missing in the basement floor or under a vanity.
5. Note WHEN it smells: all the time = trap/seal; only when fixtures drain or wind blows = vent stack issue on the roof.
6. If it's the vent, a pro snaking the roof vent ($150–$400) beats masking it with sprays.

Red flags — stop and call a pro

• Smell plus multiple slow drains and gurgling — main line problem, get a camera look
• Sewer gas smell after a heavy freeze — blocked roof vent (frost or nest)
• Smell concentrated at one wall, not a fixture — possible cracked pipe in the wall
• Anyone in the house with persistent headaches plus the smell — get it checked today

Prevention

Pour a gallon of water down unused drains monthly, clean sink overflows seasonally, and have the wax ring replaced whenever a toilet is pulled for any reason.

This guide is maintained by the ee.ltd editorial team — reviewed for 2026. Browse all home repair guides or compare plumbing costs.

Related guides

• Water heater leaking from the bottom: what to do right now
• Sudden low water pressure in the whole house: diagnosis
• Clogged drain: when to plunge, snake, or call a pro
• Toilet keeps running: the 3 parts to check

What this repair typically costs

• Water heater replacement cost guide
• Water heater repair cost guide
• Toilet installation cost guide
• Faucet replacement cost guide