Sewer Smell in the Basement? Why and What to Do


A sewer smell in the basement can be unpleasant and may indicate underlying plumbing or drainage issues. Here’s a brief summary of why it might occur and what to do about it:

Causes of Sewer Smell in the Basement

  • Dried P-Traps: The most common cause is dried-out P-traps, which are U-shaped pipes designed to hold water to block sewer gas odors from entering your home. If basement floor drains or unused fixtures don’t receive regular water flow, the P-trap water can evaporate, allowing sewer odors to escape.
  • Sewer Line Issues: Cracks, blockages, or leaks in the main sewer line can lead to the release of sewer gases, which can then rise into the basement.
  • Blocked Vent Pipes: Plumbing systems rely on vent pipes to maintain proper air pressure and prevent sewer gas from entering your home. If these vent pipes become blocked or clogged, it can result in sewer odors.

What to Do About Sewer Smell in the Basement

  • Check and Restore P-Traps: Ensure that floor drains, unused fixtures, and basement sinks receive regular water flow to maintain the water barrier in their P-traps and prevent sewer gas odors.
  • Inspect the Sewer Line: If you suspect problems with the main sewer line, such as cracks or blockages, it’s essential to have a professional plumber inspect and address the issue.
  • Clear Vent Pipes: Verify that roof vent pipes are free from obstructions like debris or bird nests. If blocked, clear the vent pipe or seek professional assistance.
  • Sump Pump Maintenance: If you have a sump pump in the basement, ensure it’s functioning correctly, as it can help manage excess water and prevent sewer gas infiltration.
  • Plumbing Inspection: Regular plumbing inspections can help identify and address potential problems before they result in sewer odors.
  • Seal Floor Drains: For floor drains that aren’t frequently used, consider covering them with a rubber stopper or plug to prevent sewer gas entry.
  • Yard Drainage Improvement: Enhancing yard drainage can help prevent rainwater from saturating the soil around sewer pipes, reducing the likelihood of sewer gas infiltration.

1. Dried Basement Floor Drain Trap

Your basement being the lowest level of your house is designed with a floor drain in mind which is connected to the sewer line. The floor drain is meant to prevent the basement from flooding by channeling excess water to the sewer line.

In plumbing, every drain line connected to the sewer line needs to have a drain trap also known as a P-trap. As such, every fixture in your house has a drain trap.

A P-trap is a U-shaped piece of pipe which also resembles an inverted P and hence its name. You can clearly see it under your kitchen or bathroom sink but cannot see the one in your basement floor drain or in shower/tub drain.


The shape of a P-trap allows it to hold water at all times. This is the water you see at the bottom of a toilet bowl at all times.

The water in the P-trap acts as a barrier preventing sewer gases from coming up through the drain. Instead, sewer gases flow out through the plumbing vent which runs through the roof of the house.

If your floor drain has not been used for some time, the water in the P-trap is bound to evaporate. When that happens, the sewer gas barrier will have been broken allowing the sewer gases to flow through it and hence the sewage smell in the basement.

The solution for this problem is usually a very easy one. You will only need to pour about a gallon of water down the floor drain to replace the evaporated water in the P-trap.

If you have other fixtures in the basement like toilets, sinks and washers that you have also not used in a while, they could also be the cause of the sewer gas smell.

Flush the toilets and turn on faucets on the sinks for a few seconds. This should solve the problem for you.

2. Missing Sewer Cleanout Plug


Sewer lines have a cleanout which is basically a pipe used to access the entire sewer line when you want to have it inspected or unclogged.

In some houses, the cleanout is located outside the house but in some the cleanout is inside the house usually in the basement. The cleanout is found inside the floor drain on the side.

It is usually covered by a plug to prevent sewer gases from coming up through it. If the plug is missing, damaged or loose, sewer gases will flow from the sewer line to your basement without being restricted.

Start by removing the basement floor drain grate then check on the side to see if the plug is there. If it is missing or damaged, you can buy another one and replace it in minutes.

3. A Bad Toilet Wax Ring

Do you have a toilet in your basement? If you do and the sewage smell in there is not caused by dried drain traps or a missing cleanout plug, you could be having a toilet wax ring that is not sealing.

A toilet wax ring is a round ring of wax that is used to create a watertight seal between the bottom of the toilet and the top of the closet flange. Although a wax ring can last for a long time, a wobbly toilet or an uneven floor can cause the wax ring to stop sealing thereby allowing sewer gases to penetrate between it and the toilet.

A bad wax ring will need to be replaced.

Start by turning off water to the toilet then flush the toilet and drain all the water from the tank and the bowl. When that is done, use a wrench to loosen the bolts on each side of the toilet then rock it about and lift it off.

Scrape off old wax from the bottom of the toilet and the top of the closet flange. Set a new wax ring on top of the flange then gently place the toilet on top. Tighten the bolts and turn the water back on.

4. Ejector Pit Not Sealed Properly

Wastewater from your house is designed to flow out to the city sewer lines or septic tank via gravity. If you have a bathroom in the basement, the waste cannot move out via gravity and you will therefore have an ejector pit and pump.

Once the wastewater flows inside the pit, the pump pumps it out into the sewer line. To prevent the ejector pit from smelling, it is usually covered with a sealed lid and vented as well.

If the lid is not sitting properly on top of the pit, the seal is broken or if the vent is clogged, sewer gases will find a way to your basement and hence the sewage smell.

The first thing you need to do is make sure that your ejector pit’s lid is properly installed and that the seal is intact. The next thing you will need to do is make sure that both the vent and water discharge pipes are not cracked or clogged.

If they are, you will need to unclog them or replace if they are cracked.  You may need to hire a professional plumber for this kind of a job.

6. Damaged Sewer Line


If you have tried all of the above remedies but still the sewage smell persist in your basement, you could be dealing with a broken sewer line.

A broken sewer line needs a professional plumber to figure out and fix. A DIY is not recommended and you may even make the problem worse than it originally was.

The first thing the plumber will do is run a sewer line inspection camera to check the condition of the sewer line. If the sewer line is broken they will be able to see although it is sometimes hard to see leaks using the camera.

In modern plumbing, a damaged sewer line does not need to be dug out and replaced. Trenchless sewer replacement is a fast, effective and cheaper way of fixing broken sewer lines. The 2 main methods used are pipe bursting and structural pipe lining.

Wrap Up

And basically that is how to get rid of a sewage smell in your basement. In most of the times, you will be able to fix the problem by simply pouring some water down the basement floor drain.

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