How to Locate Sewer Odor in the Basement

Sewer drains can allow odors into the home.

Foul smelling odors inside the basement are a sure sign that something is wrong with the plumbing. While it may indicate a clogged sewer line, it can also simply mean the air trap that prevents gas from leaking into the house has malfunctioned. But before you can diagnose the problem, you must locate where the smell is coming from. There are several locations in a basement where sewer smells can originate.

Things You'll Need

• Screwdriver
• Replacement drainage plug

Instructions

1. Close all doors inside the basement, thus shutting off rooms such as bathrooms, utility rooms, etc. Allow the doors to remain shut for several hours, and then go back into the basement. Pay special attention to the smell of the general basement area, and then open one door at a time. This will help you narrow down exactly which part of the basement the sewer odor is coming from.

2. Go into the bathroom, if applicable, and look for small pools of water around the base of the toilet. Place your hands on either side of the toilet bowl and try to gently rock the toilet. If you see water, or if the toilet rocks, the wax seal under the toilet is bad and is allowing sewer gas into the house.

3. Look for a drainage grate in the floor of the basement, if applicable. Use a screwdriver to remove the screws in the grate, and lift it up out of the floor. Look approximately 4 to 6 inches inside the drain line for a rubber plug that closes to block the sewer gas. If the plug is missing or visibly disintegrating, you have found the source of the odor. Buy a replacement plug at the hardware store.

4. Turn on all water faucets, one at a time, for approximately 30 seconds each time. In addition, flush all toilets in the basement once. If the sewer smell goes away after doing this, then the water had evaporated from the air trap under one of the sinks or toilets. The new water will create a seal blocking the sewer gas. This usually occurs in basements that are not used often.

5. Close all air conditioning and heater vents in the basement for half a day, and then reopen them. Determine whether the sewer smell is present only when the air is circulating. If so, you may have a cracked or clogged air vent that extends from the plumbing line through the roof. Call a plumber who can test the vents with a special machine.

References

• Ask the Builder: Sewer Gas Smell
• Family Handyman: How to Eliminate Basement Odor and Sewer Smells