How to get rid of flies in a composting toilet

A question that comes up from time to time is “I have flies (or gnats or whatever) in my composting toilet. How do I get rid of them?” In my experience, about one person in 20-30 eventually has this problem, so you are not alone. The good news is, you can easily get rid of flies and dramatically reduce the chance of getting them again.

New product: Recently a new product has been introduced that is reportedly highly effective for getting rid of flies in composting toilets. It is 100% organic, natural and non toxic, and smells like lavender. Bin Breeze. It’s a combination of 3 natural products – diatomaceous earth, a mineral called zeolite (found in volcanic ash), and untreated wood waste. Preliminary testing has been very promising.
The first step is to eliminate potential sources of flies in the home. The toilet does not produce flies, and there should not be flies or fly eggs in human waste. That means the flies came in from somewhere else. Fruit bowls are a big culprit. Once in the home, flies will be attracted to the toilet, where they lay eggs and multiply. Before leaving your cottage, eliminate all possible sources of flies, including garbage (not even an apple core should be left behind) or compost.

Nature's Head fan housing

Nature’s Head fan housing

The second thing you do is make the toilet unattractive or unavailable to the flies. Clean the toilet very well inside, in every nook and cranny, with something that will kill fly eggs like a mild bleach solution. Water and vinegar will not work.

Don’t get the fan wet. With the Nature’s Head you can remove the fan housing and hose it all down outside, after using the bleach. However, the Separett fan housing is a bit of work to remove, so it’s best to clean the toilet with the fan housing in place.

Add about 5 cups of diatomaceous earth to the new coconut coir in the Nature’s Head, or with the Separett add a cup per week to the removable bucket. You may have to experiment a bit for the optimal quantity.

diatomaceous earth

diatomaceous earth

Diatomaceous earth is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It is a very good natural insecticide. This will solve the fly problem 99% of the time. It is not expensive and commonly available.

Be sure the fan screens are clean, unobstructed, and pumping air. You should be able to feel air being blown out at the exhaust vent.

As a very last resort, you can put a small “mothball cake” in the lower part of the toilet. The fan should exhaust the odor, and you should not smell mothballs in your home. This will definitely stop all flies.

moth cake for composting toilet

moth cake for composting toilet

However, mothballs contain a chemical insecticide, and therefore must be used cautiously.

Once you do these things, I am quite sure you will have no more fly problems. Cleanliness and removing the source of flies is by far the most important step.

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4 thoughts on “How to get rid of flies in a composting toilet

  • Trudy Bradt

    Hello….we have a moth problem with our composting toilet. They seem to be hatching in it. We see them flying up out of the toilet and we’re greeted with many of them flying around the room every time we open the door. We are wondering what we can safely spray in it to kill them that won’t harm the way the toilet works. Thank you in advance.

    • Richard Post author

      Follow the same instructions as with flies. You should clean out the toilet. Moth balls, insect spray etc. will not harm the toilet.

  • Karen Gruhl

    Our composting toilet is at our camp (cottage). It is non-electric, so no fan and also in its own separate building (not in the cottage). I think they are fruit flies but am perplexed as to why they were attracted to the toilet? We have two composting toilets and only one has flies. Any suggestions? I can try bleach solution. Thanks.

    • Richard Post author

      Please see my page on how to get rid of flies in a composting toilet. I don’t have any non-electric toilets, so I’m not sure what brand you are using. I tell people that they can try using the toilet with a vent only (in an outhouse) but there is no guarantee of success. A fan is often required, even in an outhouse – and 100% of the time in a home. I know many people don’t want to power their toilet, but this can result in odor and insects. I would not believe any claims from sellers that you can have a composting toilet without a fan. Some toilets don’t even have vents (which is beyond ridiculous).