Sump Pump Smells Like Sewer, Rotten Eggs, Gas, Dead Animal

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Many homeowners simply ignore the sump pump until a problem occurs. If sump pumps are not maintained properly, which includes being cleaned regularly, they can start to smell and stink. Home ownership requires knowing how to prevent the sump pump from smelling.

If left unchecked, not only can sump pump odors result in the entire basement to start stinking, but they can also creep from the sump basin and permeate your house.

If you start noticing unpleasant odors coming from your crawl space or basement, they may come from the sump pump. A sulfurous smell coming from the sump pump is often simply an indication that minor maintenance is required.

A foul odor can however sometimes be an indication that you have a more serious problem with your sewer line.

You may have foul sump pump odors that don’t want to go away and your basement sump pump smells like rotten eggs, sewage, or any stinky smell.

If this is happening to you, read on, as we’ll discuss the most common issues that may cause your sump pump to smell bad and how you can fix those problems fast.

Woman holding her nose. Photo credit The MomBuster
Holding your nose will not make the sump pump smells go away. Photo credit The MomBuster

Sump pump odors are often not only inconvenient, but the smells may be an indication that there is something wrong with your sump pump.

Fortunately, sump pump smells are often early indications of a problem. It’s much better to discover that a sump pump has an issue via a foul smell rather than the basement flooding.

What Causes a Sump Pump Smells?

Standing Water

A sump pump pit collects water until it rises to a specific level, at which stage the pump float will switch the pump on and the water will be pumped out of the pit. If this happens regularly, the water is pumped out frequently and fresh incoming water replaces it.

If groundwater infiltration is however minimal, the pump will not switch on for long periods. This will allow the water collected in the basin to turn stagnant and develop mildew or mold that creates smelly odors.

Some things that may cause the water to smell bad include:

  • When all the water isn’t pumped out of the basin, the residue will sit undisturbed for a long period. Not only will this emit a musty, stagnant, and stale water odor, but it will also create the ideal conditions for mildew and mold to grow.
  • If water is left standing in the bottom of the pit, all types of bacteria will breed which will create its own odor.
  • When there isn’t much activity with rain during a dry season, residual water in a sump pump pit will evaporate slowly and leave the walls damp, once again creating an ideal environment for mold.

Mildew and mold can fortunately be killed by bleach easily. Here are two DIY solutions to eliminate the odors:

  • Pouring five gallons of clean water into the basin will actuate the float switch and the stagnant water will be pumped out. You might want to use a second or third bucket of water to help clean the pump and sump pump basin a little better.
  • Once the water has been removed, pour a quart of bleach, diluted 50/50, into the residual water still left in the basin.

Sump Pump Smells Like Rotten Eggs

This is actually a sulfur smell that comes from your sump pump.

It is well known that a sump pump smells for several different reasons, of which the most common is due to dirt containing decaying organic matter building up.

What a rotten egg looks like. Image credit @jeanelleats
What a rotten egg looks like. Image credit @jeanelleats

Issues With Sewage

Rainwater is unfortunately not the only thing that your sump pump may be gathering from the earth around the home. A sulfurous smell is sometimes indicative of a more serious problem than simply stagnant water.

The sump pump collects groundwater from under the home’s foundation and then pumps the water away from the house.

If a sewer line is broken, it will saturate the groundwater around the home with sewage. Some of the water flowing into the sump pump will therefore contain sewage waste, which would leave a sewage residue that smells foul.

The odor will start when the contaminated groundwater has seeped into the sump pit and your sump pump smells like sewer.

In the beginning, a smelly sump pump caused by a sewer line break won’t be constant. Although you may only notice the bad smell from your sump pit every now and then, it will eventually become a steady odor.

To remove a sewage smell from the home, the sewer line must be repaired, and the sump pump cleaned or replaced. It’s best to get a professional involved to do this as soon as possible.

Plumbers often use cameras for sewer line inspection to find where the leak or rupture is located. They can then do the repairs required to prevent future sewage contamination in the groundwater and the sump pump smells like sewage problem.

Sump Pump Smells Like Gas?

Natural Gas

While sewage gas smells like rotten eggs, a natural gas smell is often described as smelling like a skunk. If your sump pump smells like gas, call the gas company immediately. If you can’t reach them, call your local fire department.


If Gasoline is spilled on the soil close to a basement wall, it can easily seep into your basement and emerge as fumes.

A gas station across the street might have a gas tank leak that is contaminating the ground.

Broken or Cracked Equipment or Pipes

In some cases, a foul-smelling sump pump may indicate that part of your plumbing is broken or cracked. This may either be directly on your sump pump or in the plumbing system itself. Either way, this will cause major problems for the sump pump.

Clogged Sump Pump

If a sump pump drainage system is clogged, it needs to be taken apart, the pump removed, and a thorough inspection of the pipes and propellers performed to ensure nothing is clogged or jammed in the sump pump.

Mechanical Issues

The sump pump may experience mechanical operational issues. As any moving parts could potentially fail, this could result in water not getting pumped as it should. This will in turn create a stagnant pool of water with bad sump pump smells.

Sump Pump Lid Not Sealing Properly

An improper seal on the sump pump lid is another common problem that may lead to bad odors and smells. Sump pumps should be fitted with lids with watertight seals.

The lid’s purpose is to prevent radon gas or other gasses from leaking from the sump pit and into the living space.

If the seal wasn’t fitted properly or is cracked, smelly gasses will escape from the sump leading to bad smells in the basement.

The Original Radon Sump Pump Lid (shown below). Will replace any standard sump pump cover.

No products found.

If a lid is broken or cracked, you may be able to seal the cracks with watertight silicone adhesive. If that doesn’t work, you’ll have to purchase and install a new sump lid.

Related article: 4 Radon Cover for Sump Pump Reviews: Jackel vs RadonAway

Burnt out Sump Pump

A sump pump that is completely burnt out can also cause bad smells. Sump pumps normally last for about 8 to 12 years depending on the brand and model. A sump pump that is burnt out and can no longer work won’t pump the water from the basement. This will lead to odors, foul smells, and flooding.

The solution is to simply remove the old pump and replace it with a new one.

Sump Pump Smells Like Dead Animal?

If your sump pump smells like a dead animal, it’s pretty unmistakable.

There are many places in your house that a little animal can get into. It’s not likely that they’ll come in through the sump pump, but they may come into the sump pump to get to the water.

If they come there to drink, they may not be able to get out of the pit and end up drowning. This will however result in a mess that has to be cleaned up.

One easy way to get rid of the dead animal is to use a small bucket or a net to scoop it up and take it outside.

The sump pit and pump should also be cleaned after the animal has been removed to get rid of the lingering bad smell.

4 Ways to Deodorize Your Sump Pump

1. Flush Out Stagnant Water

Smells are commonly caused by stagnant water rotting in the basin below the level at which the float switch will activate. Pour water into the sump basin to flush out the old water by letting the sump pump operate like normal. In minor situations this might be all that is needed.

2. Use a Basin Cover

Always use an airtight cover to prevent smells from escaping out of the sump pit. This will result in fewer smells being able to creep into your home.

Although airtight covers work best, one with a perfect fit with the seal fitting as tight as possible will also do the job.

The RadonAway sump pump cover with clear plastic inspection window. See it below.

Radon Mitigation Sump Pump Dome Cover Lid with Window to see sump pump and water level by RadonAway Radon Away
  • 24″ Outside diameter
  • Easily removed without pump removal
  • Strong center brace
  • Plastic window for easy viewing inside of sump pit

3. Disinfect with Bleach

Use a solution of 1 cup of bleach for every gallon of fresh water to clean your sump basin and pump. This will kill the bacteria that cause smells and keep everything sanitary.

As the bleach is diluted with water, the solution won’t damage the sump pump if it isn’t pumped out of the basin fully.

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Sump pumps are usually made from stainless steel, thermoplastic, cast iron and even bronze. All of these can be cleaned safely with diluted bleach.

4. Clean Sump Pumps with Vinegar

Although it may surprise you to hear that cleaning a sump pump pit with vinegar is recommended, it is a very good solution to remove stinky smells such as poop, rotten eggs, and dead animals.

Pour at least 5 gallons of water into the sump basin to flush it and allow the sump pump to pump it out of the house.

Scrub the sump basin and pump with a 50/50 solution of hot water and vinegar. If more cleaning power is required, add some liquid dish soap.

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Scrub the exterior of the sump pump as well as the whole sump pump basin. Then flush it all out by pouring in at least 5 gallons of clean water. That will prevent the vinegar from causing rust and corrosion.

Last update on 2024-05-24 / Affiliate links / Images from Amazon Product Advertising API

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