A Sewer Smell in a Basement Drain When Taking a Shower

Sewer gases may escape from some drains.

Sewage creates a wide range of gases, such as methane. These gases produce strong smells that can travel back up discharge pipes and basement drains. Usually, drain systems are designed to block these gases from being released into your home. But there are some problems that can allow sewer gases to escape.

Faulty Cleanout Plug

Many basement drains contain a cleanout plug. These are plastic or metal plugs that screw into place at an angle just after the drain grate. If the plug is not screwed in all the way, or if the plug is damaged, the sewer gases that it normally blocks may escape from the drain. Check the plug by removing the drain grate and physically inspecting the condition of the plug. If the plug is damaged or has corroded seals around the edge, replace it with a new plug.

Water Trap

Most floor drains contain a P-trap. The P-trap is a bent pipe that allows water to pool in the bottom. This water blocks sewer gases from coming back up the pipe. However, the water inside these traps will evaporate over time. Pour a bucket full of water down floor drains every six months or so to restore the water trap and eliminate the odor. Pour a couple tablespoons of cooking oil down the trap after flushing with water to help prevent the drain from drying out so quickly.

Toilet Wax Ring

Some basement drains are connected to toilets. All toilets contain a ring made out of wax that sits under the bowl. The wax ring seals the connection between the toilet flange and the bowl. The ring also prevents sewer gases from escaping from around the flange. If the seal is dry, cracked or broken, remove the toilet and replace it with a new one. Wax rings should normally be replaced every 10 years. Toilets that are loose and rock back and forth may lead to broken wax rings. Shim your toilet to prevent rocking.

Broken Pipes

If any of your waste drain pipes have cracked or broken due to freezing or corrosion, it's possible that the smell of sewer gases is coming from there. Cracked pipes that are installed under basement floors may require major repairs, including removal of the floor. Because some sewer gases, such as methane, are potentially dangerous, it's important to hunt down these leaks as quickly as possible. Rent a pipe scope from your hardware store to view the inside of the drain and check for signs of damage.

References

• The Family Handyman: How to Eliminate Basement Odor and Sewer Smells
• The Restoration Resource: Broken Sewer Lines -- The Health Risks and How to Fix the Damages It Caused