How to Reduce Septic Tank Odor

August 22, 2022

A properly functioning septic tank should be odor-free, so if you notice a bad smell inside your home or outside near the leach field, it’s a sign there’s a problem.

A foul smell doesn’t necessarily mean the septic tank needs to be pumped, however. Septic odors are caused by gases in the system, including carbon dioxide, hydrogen sulfide, and methane. In high concentrations, these gases can be toxic and potentially explosive. Here are some common causes and solutions for septic tank odor.

Septic Odors Inside the Home

A septic odor in your home usually means there’s a plumbing problem.

  • The floor drain trap in your basement could be dried out, allowing septic tank gases to vent back into your house. Periodically filling the drain traps with water will correct the problem.
  • The cleanout access plug, located inside the drain, could be loose and allowing sewer gas to leak. Call a licensed plumber to clean the line and check the plug.
  • The plumbing vent on the roof could be clogged or blocked. The vent equalizes the pressure in the drain pipes as wastewater moves through. If your tub, sinks and toilets are gurgling, this could be the culprit. If the vent has just frozen shut, it will thaw when the temperature warms up. However, if leaves, a bird nest, or some other debris is clogging the vent, they’ll need to be cleared out. When climbing on the roof, be sure to take precautions to prevent falls.
  • The ejector sump pump basket may not be properly sealed. Check the cover, and apply a new seal to prevent further leaks.
  • If the odor is most noticeable in the bathroom, it could just be a dried out toilet wax seal. Simply remove the toilet and install a new wax ring. You can stack two seals on top of each other if the toilet flange was not raised above the ceramic tile floor.
  • A less likely cause is a hole or leak in a plumbing joint, drain line, or under a sink.

Odor Near the Septic Tank Outside the Home

It’s normal to occasionally notice a weak smell near the septic tank, but a strong odor could be a sign of a leak from the manhole.

Septic Tank Door
  • Check the risers and manholes to make sure they’re covered securely. The tank manhole cover is usually a concrete lid, but it could also be metal or plastic. A septic tank manhole could be buried under as much as a foot of soil, except in the case of tanks with sump pumps, which must be at the surface so the pump can be repaired or replaced.
  • A plastic manhole lid will have a rubber seal to keep odors inside the tank. The lid is also secured with fasteners such as lag screws.
  • A concrete manhole lid that’s leaking can be temporarily sealed with weather stripping to contain the odors until the tank can be repaired. After the tank is serviced, the permanent seal will need to be replaced.

Leach Field Odors

The soil treatment area, or leach field, consists of an in-ground drain bed, field, or mound, and there should not be a strong septic odor unless there’s a problem.

  • Have septic system pipes inspected to ensure there are no crushed or broken spots.
  • Have a professional plumber check for roots growing into the pipes and causing a blockage.
  • Do a visual inspection of the leach field to look for areas of soggy or wet soil, which is an indicator that sewage is rising to the ground’s surface.
  • Regardless of the cause, leaking sewage is considered to be an imminent threat to the health of both animals and humans, so the issue should be fixed immediately by a licensed plumber.

Odor in Other Areas Outside your Home

If there’s just a general sewage or septic smell in your yard or outdoor areas, the plumbing vent pipe may not be long enough to fully diffuse the odors.

  • If your home is located in a low-lying area, a valley, or is surrounded by lots of trees there may not be enough winds to disperse the odors away from your outdoor living space.
  • Having a plumber extend the plumbing vent pipe can help the wind diffuse odors better.
  • Have a carbon filter added to the top of the plumbing vent to reduce septic odors. For maximum effectiveness, the filters will need to be changed approximately every 1 – 5 years.

Odors Caused by Improper Tank Chemistry

Inside the septic tank, microbes work to break down waste solids. In order for this bacteria to survive and do their job, the pH level must be maintained between 6.8 and 7.6. If it becomes to acidic, a strong hydrogen sulfide gas odor (like rotten eggs) can develop.

  • Never flush non-organic waste down the toilet, such as cigarette butts, feminine hygiene products, and trash.
  • Avoid pouring fats, oils, coffee grounds, cleaning products, paints, or other chemicals down your sink or tub drains. These can disrupt sewage breakdown inside the tank and cause a foul odor.
  • Adding a cup of baking soda to a sink drain or toilet once a week will help maintain the correct pH level in the septic tank.

To keep your septic system odor-free and working properly, have a professional plumbing service, like Bailey Brothers, clean out the septic tank every 3 – 5 years.

Our goal to provide only current and accurate information on our site. However, this site could contain information that is out of date, or incorrect for your specific situation. Please note that all resources found here are for general information, they are in no way a guide. Bailey Brothers Plumbing Heating and Air Conditioning does not assume any liability problems resulting from incorrect information provided here. If you attempt to work on your own plumbing, HVAC equipment, always consult your equipment’s operating manual, and only do so if you are qualified.