Getting Rid of a Sewer Smell in the Basement

Updated: Feb. 15, 2023

Stop sewer gas from entering the basement.

No one wants to have a musty basement. If you notice foul sewer smells in your house or basement, here are the five possible causes in order of probability. Plus, we’ve included some tips to eliminate sewer smells and unpleasant odors. Bonus: We’ve rounded up the best basement odor eliminators for the job, too.

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A Dry Water Trap is Causing the Sewer Smell

The most likely cause is a water trap under a floor drain, laundry tub or wash basin that has dried out from lack of use. Water in any trap under unused drains will eventually evaporate. That would allow sewer gas to come up through the drain into the room.

Solve that problem just by dumping a pitcherful of water into the drain to restore the trap water. If you follow that up by pouring a couple of tablespoons of cooking oil into the drain, a floating seal of oil will keep the water from evaporating so fast next time. Also, learn how to get rid of the shower drain smell.

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Sewer Smells Caused by a Missing Cleanout Plug

Check for a cleanout plug inside the floor drain to get rid of a sewer smell in bathroom or laundry room. Remove the grate that covers the opening and make sure there’s a plug inside the drain bowl. If the plug is missing, there’s a direct path for sewer gas to bypass the water trap. Sometimes, the plugs are removed to clean sewer lines and not replaced. Buy a replacement plug at a hardware store.

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Dry Toilet Trap

It’s less likely, but the water in the toilet trap also could have evaporated. Weeks of disuse could cause this. Of course, simple flushing will restore that water and should eliminate the foul smell.

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Leaky Wax Ring

Another culprit for a sewer smell in a bathroom could be a bad wax ring seal between the toilet flange and the base of the toilet. This wax ring can occasionally leak, sometimes because of a rocking toilet that has broken the seal. With a leak in this seal, sewer gas will find its way out from under the toilet.

If that’s the case, you’ll have to remove the toilet and replace the wax ring. If the toilet rocks, use plastic shims between the stool and the floor and caulk the joint. This will ensure that a rocking toilet doesn’t ruin the new wax ring.

Plumber in a blue shirt is working on a sewerDouble_H/Shutterstock

Cracked Lines Causing Sewer Smells

A more serious prospect for the sewer smell in your house would be a broken or cracked sewer line or even a loose connection joint in the ceiling or buried in a wall. If you’ve addressed the four easier possibilities, use your nose to start investigating, starting with all visible joints. If you can’t detect the leak, contact a plumber who specializes in hunting down leaks.