What is that sewer smell?

Sewer smell coming from your sink doesn’t always mean something’s broken, but it does mean that some part of the plumbing system isn’t functioning properly.

Sewer gas is supposed to go up and out, so your home is designed with vent pipes to vent that gas at the top of your house. You might see these pipes on the outside of your house, or just vents on the roof. See the yellow vent pipes on our simple illustration of a home sanitary system design on our Plumbing page.

A common reason for sewer smell is a sink or drain that isn’t used frequently. If not used, the P-Trap under the drain lacks enough water to block the sewer gas from escaping. This happens to guest bathrooms and powder room toilets that aren’t used often, and to basement floor drains. The P-Traps under these drains lose water by evaporation, so sewer gas seeps back through the line into the house. Flush, wash your hands, pour mop water down that basement floor drain – use those fixtures once in a while.

But something could be broken if there’s sewer gas smell in the house. A fixture vent might be damaged or blocked, which can cause a P-Trap to lose water by suction. The P-Trap could be damaged or loose. The problem could also be in the sewer line – a Pipe Spy sewer line video inspection can help to diagnose a solution to your sewer smell problem.