Why Does My Sump Pump Smell Like Sewage?

An odor coming from your sump pump is its way of telling you that something is wrong.

As these devices are installed in basements and concealed, it is normal for them to go through long periods of time without being inspected or checked. 

However, you’ll be happy to know that an unpleasant odor is more of a warning sign, and it’s always better to find yourself with a smelly sump pump indicating there’s an issue, rather than a flooded basement

This article is going to be explaining a few reasons why your sump pump may smell like sewage and what you can do to fix it. 


What Is A Sump Pump, And What Do They Do? 

Before we delve deep into the world of sump pump smells and issues, let’s explain what they are and what they do. 

A sump pump collects water that accumulates in your home and transfers it away in order to prevent any flooding.

The sump pump is usually installed in the lowest part of a basement in a sump pit that has usually been constructed especially for it. 

Water will then make its way to this sump pit, and once it reaches a certain level.

The sump pump will get to work by pumping the water out of the pit and transferring it away through drainage pipes that will transfer the water away from your home. 

They are usually activated by a float. Once the water rises, the float will rise too, and once it rises higher than a certain point, the pump will switch on and start pumping out the water. 

Common Smells From Sump Pumps

Aside from smelling like sewage, other smells could accumulate in your home or basement if your sump pump has an issue. Below are some common ones: 


This is a common smell that your sump pump is likely to be associated with, as this device constantly holds water.

This results in mold and mildew growing inside it. Therefore, ensuring that the machine dries properly is the key to avoiding this issue. 


If your sump pump has dried out, then gasses from sewers can pass through and leak into your garage and home.

This smell may resemble gasoline, and can sometimes contain toxic gasses, so if you begin to smell gas coming from your sump pump, you must call a professional immediately. 


Waste will normally enter your sump pump, and occasionally this can cause a build-up and unwanted clogs.

Fortunately, when this is causing an odor, normally, all that your sump pump needs is a good clean and the smell should disappear. 


You may experience odors resembling rotten eggs. If you do, this is likely to be sulfur caused by a build-up of dirt. 

Issues That Will Cause Your Sump Pump To Smell

How To Remove Sump Pump Odors

As mentioned earlier, detecting a smell from your sump pump is the first indication of an issue, and there could be a number of reasons for this.

Below are some common causes of smelly sump pumps. 

Sewage Infiltration

If you are noticing a smell that resembles sewage, then there may be a broken sewer line around the foundation of your sump pump. 

This could result in sewage leaking into the sump basin and once this happens, a sewage smell will begin to be emitted.

When this problem begins, you may only notice the sewage smell occasionally before it becomes constant. 

Therefore, the minute you notice a smell resembling sewage, you should call a plumber immediately to inspect your sump pump. 

Stagnant Water

Your sump pump will only be activated once the water level that has accumulated reaches a certain level. Once it does, the float will activate the pump to start working.

However, if the float isn’t working accordingly, or the sump pump isn’t running properly, this could lead to the basin not emptying properly which leads to stagnant water, which creates unpleasant odors. 

This could also be due to not enough water filtering into the sump pump.

If enough water is entering, then the pump is activated regularly and old water is flushed out and replaced with fresh water.

If there isn’t enough water entering the sump pump regularly, then that means the pump won’t switch on enough, leading to previous water remaining in the basin. 

This water that lays stagnant can accumulate mold and mildew, which releases odors that aren’t pleasant around your garage and may eventually leak into your home. 

While this is an issue, there are a few ways you can resolve this problem without having to call a professional. 

One solution is to pour a few gallons of freshwater into the basin, around five of them. This should activate the float switch to get the pump working on flushing out the stagnant water.

Once this water has been flushed out, pour diluted bleach into the remaining water that’s in the basin. 

Basement Drainage

Some sump pumps take on water from laundry units and showers, and these sump pumps are used to drain greywater.

This means that they will take on quite a lot of residue from these items, and over time they lead to a buildup that releases odors. 

This is where cleaning your sump pump and pit comes in handy, as it will get rid of the smell. 

How To Solve The Problem

If there are unpleasant odors in your home caused by your sump pump, you should always call a professional.

They have the appropriate training and tools in order to determine the best cause of action. 

They may be able to complete a thorough cleaning of your sump pump, or repair any leaks if that is what is causing the problem. 

If the issue is more extensive, they may recommend you replace your sump pump altogether. 

If you’d like to try and solve the problem yourself, you could pour a diluted bleach solution down your sump pump in order for it to switch on. 

You could also scrub the walls of the pit with this bleach solution, and this may get rid of the unpleasant smell. 

Final Thoughts 

To conclude, an unpleasant smell will most likely indicate there is a problem with your sump pump.

If you catch the issue early enough, the problem should be solved daily quickly by a professional plumber. 



Bill is a DIY plumber, handyman, and homeowner with more than a decade of experience. He has replaced and repaired sump pumps, backup pumps, float switches, check valves, and many other things around his family home. An engineer and tinkerer at heart, he is always looking to see how things work and taking on new home projects that help him grow his skillsets. He is a husband and father of two boys, has a bachelors degree in Computer Engineer and minor in Mathematics and likes to make homebrew beer in his free time.

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