4 Practical Steps To Keep Drain Flies Out Of Your Sump Pump

Having a sump pump in your basement always seems like a good idea. It’ll help remove any moisture and reduce the chance of flooding. However, now you may notice that strange black flies are flying in and out of your sump pump. If this is the case, then it sounds like you may have a slight drain fly infestation.

In this article, you’re going to find out exactly what you need to do to remove drain flies from your sump pump and stop them from spreading to the rest of your house!

So without further ado, here’s a step-by-step guide to keeping drain flies out of your sump pump.

First Of All, Is It Even Possible For Drain Flies To Come From Your Sump Pump?

Yes, it’s entirely possible that drain flies can come from your sump pump. They’re attracted to standing water, precisely like the water found in the pit that houses your sump pump. This is because the standing water and the decaying organic materials create the perfect breeding ground and habitat for them.

How To Keep Flies Out Of Your Sump Pump

If you have drain flies in your sump pump, the first thing you’ll need to do is remove them. Before focusing on making sure they don’t come back! So, step 1…

1. Drain The Pit Of Your Sump Pump

The first thing to do is drain all of the water from the pit of your sump pump. And when I say all of the water, I mean all of the water. Drain flies can breed in small amounts of water, so you need to make sure the pit is as dry as possible, thus removing their natural habitat.

Most sump pumps are automatic and will only start draining once the water hits a certain level. So you may have to turn the sump pump on manually to get rid of it all.

Whatever water is left at the bottom, you should try to remove it with a towel or scoop of some kind.

2. Clean The Sump Pump Pit

The next step is to make sure that the sump pump pit is clean. Drain flies like stagnant water full of organic material to help them breed and eat. So you’ll need to get rid of both. To clean the pit, all you need to do is use soapy, warm water and a scrub brush to give it a thorough clean.

During this time, you should also make sure you’re killing any drain fly larvae that are living in the pit as well. They’ll be clinging to the wall and look like pale, translucent cylinders with black heads. You may need to use a torch to see them better.

Stick to soapy water at this point and avoid using pesticides as you definitely don’t want to contaminate the water in the sump pump.

Once the pit is clean, use normal water to rinse the soapy water out before getting the sump pump to remove it all again. Whatever the sump pump doesn’t remove, wipe away with a towel.

To help the pit dry quicker, you can also use floor fans to evaporate any water.

Adult Bathroom Moth Midge of the species Clogmia albipunctata

3. Use An Insect Growth Regulator

The next step is to use an insect growth regulator. They’re not as strong as pesticides but are still more than capable of killing any larvae that drain flies try to lay in your sump pump pit. Not only will it kill larvae that you missed, but it will also kill any future eggs that are going to be laid.

As well as an insect growth regulator, you can also try using a foaming product as well which can get into the cracks and crevices a standard IGR may miss. For an IGR, I’d recommend ZOECON Gentrol Insect Growth Regulator, and for a foaming product, I’d recommend InVade Hot Spot.

4. Kill Any Adults You See

Now the final step to make sure the drain flies don’t continue to breed and start the cycle all over again is to make sure you’re killing all of the adult drain flies. Fortunately, there are a few ways you can do this.

Swat Them

Of course, this is the easiest way to kill adult drain flies. Simply swat any of them you see flying around your sump pump to stop the cycle of breeding.

Drain Fly Trap

Another great way to kill the adults when you’ve sorted out your sump pump is to create a drain fly trap.

Drain fly traps can be used to catch drain flies that have decided to make their home around your sump pump. And to do this, all you have to do is mix equal parts sugar, water, and vinegar in a bowl before adding liquid dish soap.

Then just keep the bowl in near the sump pump for a few nights, and the drain flies will be drawn to it and die. For optimal results, leave the trap alone for a few days.

Apple Cider Vinegar & Plastic Wrap

Another option is apple cider vinegar and plastic wrap. This way is definitely a lot more hands-off but can be equally effective. Just put some apple cider vinegar in a cup and cover the top with plastic wrap. Once the plastic wrap is on, poke some small holes into it. This way, the drain flies will be able to climb through but unable to leave.

Sprays And Repellents

Lastly, we’ve talked about spraying INTO your sump pump, but you can also spray repellents and aerosols that kill drain flies AROUND your sump pump too. Just make sure when you’re using these sprays, you’re always reading the instructions to make sure they’re safe for you to sleep around.


As you can see, keeping drain flies out of your sump pump isn’t actually that hard at all. In fact, it can be an incredibly easy and quick process. It’s all about catching them early and removing them as soon as possible.

I hope this article has answered all your questions. If so, make sure to check out the rest of the website! Otherwise, have a great day!

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