Why Does my Basement Smell Like A Sewer

Your home is your castle, and you want that castle to be clean and inviting. If you walk into your basement and smell a sewage smell, then you are failing at reaching that goal. Michael Bonsby HVAC & Plumbing recently launched a new branch of our business, Michael Bonsby Plumbing & Drain Cleaning, and we would be happy to help you with this frustrating problem. We proudly serve homes in Montgomery County.

Here are some steps to troubleshoot the problem before you call.

Check for a Floor Drain

If you have a floor drain in an unfinished basement, then the only water that drain probably receives is condensate water from the furnace. Unfortunately that is not enough water to keep the drain working well, and the trap serving the drain may have dried out. Water can then stagnate in the trap, causing a putrid smell.

To fix this, you need to clean the drain thoroughly. Contact us if you need a professional to clean your home’s drains.

Check the Ejector Pit

If the drain is not the problem, check to see if you have an ejector pit. An ejector pit receives water from the laundry, bathroom, kitchen and other areas of the house, and it is supposed to send that water out of the house. You can tell if you have this if you have two pits in the basement one for the sump pump and another to handle the water.

Ejector pits are supposed to have a tightly sealed lid, but unfortunately sometimes builders or homeowners cut corners and simply install a sump pump without a lid. If this is the case, then you have found the source of your smell. To fix it, you will need to have a professional plumbing team install an ejector pump with a sealed ejector lid.

Check Basement Plumbing

Finally, check any plumbing fixtures in the basement, like your laundry room or an extra bathroom. If these were added after the home was built, they may not be properly vented. Venting these fixtures into the walls without tying the vent to something else will cause a sewer smell in the basement. Similarly, if your upper floor plumbing fixtures are not vented properly the sewage smell can seep into the basement.

Contact a Plumbing Professional at Michael Bonsby

If you have checked these three things and still are confused about your smelly basement, you need the help of a plumbing professional to scope out the problem and find a solution. Contact Michael Bonsby Plumbing & Drain Cleaning, to schedule an assessment and eliminate your smelly basement.

Sewer & Drain FAQs

Why does my basement smell like a sewer?

There are several common causes of a sewer-type smell in your basement. Many times it’s due to a dry or empty floor or sink drain trap, which allows sewer gases to enter your space. Other causes include missing or damaged clean-out plugs, cracked or leaking sewer lines, improperly sealed plumbing fixtures, or a plugged vent stack.

How do I know if the smell is coming from sewer gas or something else?

If you detect a rotten-egg or “rotten-sulfur” smell, that’s a strong sign of sewer gas caused by decomposing waste or leaking plumbing gasses. Other odors like musty or moldy smells may stem from moisture or mildew rather than the sewer system. Look for slowed drains, gurgling noises, damp spots or multiple fixtures affected—these hint toward a plumbing odor source.

What are simple things I can check myself to stop the smell?

Here are easy steps to try:

• Pour water into unused floor drains or sinks to refill the trap and restore the water-seal barrier.

• Check that clean-out plugs under floor drains are present and sealed.

• Flush rarely-used basement toilets or fixtures so their traps stay filled.

• Look for visible cracks or loose seals around toilet bases, floor drains or pipe penetrations.

If the smell lessens after these steps, you’re likely dealing with one of the simpler causes.

When is the odor a sign of a serious problem?

The odor may signal a more serious issue when you see signs like: slow or backing up drains, multiple fixtures with odor, damp spots or pooling near sewer lines, or the smell returns after refill efforts. A cracked sewer line, root infiltration, or malfunctioning venting system requires professional attention. If you suspect gas buildup (especially hydrogen sulfide or methane) or detect a strong or persistent odor, it’s time to call a qualified plumber.

How can I prevent the basement from smelling like sewer again?

Prevention involves regular maintenance and awareness:

• Run water periodically through rarely-used fixtures to keep traps filled.

• Ensure floor drains and clean-outs remain capped and sealed.

• Keep vent stacks clear of debris and ensure plumbing vents function correctly.

• Seal gaps around plumbing penetrations, warranty seals beneath toilets, and monitor sump or ejector pits for odors.

• Have a plumbing inspection if your home is older or you suspect drainage or sewer line issues.