Sewer Smell in the Basement or House: Causes and Fixes

What are the 5 causes of a sewer smell in the basement?

The 5 causes of a sewer smell in the basement are listed below.

• A dry floor drain trap lets sewer gas into the basement.
• A cracked drain pipe or sewer line leaks gas and waste.
• A loose or missing cleanout cap opens the line to the room.
• A failed toilet wax ring leaks gas at the base of the toilet.
• A blocked vent pushes sewer gas out through the traps.

Is a sewer smell in the house dangerous?

Yes, a strong sewer smell in the house is dangerous, because sewer gas contains hydrogen sulfide and methane.

What should you do first about a sewer smell?

The 4 things you should do first about a sewer smell are listed below.

1. Pour water into the basement floor drain to refill the trap.
2. Check the cleanout cap for a tight seal.
3. Open windows to air out the basement.
4. Call a plumber when the smell returns.

When should you call a plumber?

You should call a plumber in the 4 situations below.

• The smell returns after the trap is filled.
• Drains run slow with the smell.
• Sewage shows at the floor drain.
• The smell is strongest near a wall or the floor.

Related plumbing problems and next steps

How much does the plumbing repair cost?

The plumbing repair cost depends on the source: a sewer line camera inspection and repair cost more than a trap or wax ring fix, and a cracked sewer pipe repair costs $600–$1,050, according to HomeAdvisor. Sewer line repair prices and local plumbers are on the sewer line repair across Lancaster County page.

What is a related plumbing problem?

A related plumbing problem is basement floor drain backing up, and the basement floor drain backing up guide lists its causes and first steps.

Written and fact-checked by the Lancaster PA Plumbers editorial team using HomeAdvisor, EPA WaterSense and City of Lancaster data. Last updated October 29, 2026.