Can Drain Flies Come From the Toilet? Where to Check For Them

An extreme close up of a drain fly showing the fuzziness of the body and antennae.

If you’ve noticed small, gnat-like bugs buzzing around your bathroom, there’s a good chance that they’re drain flies.

The best way to get rid of drain flies is to know where they’re coming from so that you can attack them properly.

Can drain flies come from the toilet? Though drain flies are more commonly found living in sink, shower, and tub drains, occasionally they will congregate and breed in the tank or bowl area of a toilet. However, in toilets the center of activity is typically around the closet flange.

Finding bugs flying around or even out of your toilet is no one’s idea of a good time. You’ll want to get rid of them as quickly as possible.

In the following, you’ll learn where you’ll most likely discover the source of the infestation and exactly what to do to take care of the problem for good.

What Are Drain Flies?

Drain flies are technically known as Psychodidae. They are also commonly called moth flies, sewer gnats, or sink flies.

They range from 1 to 5 millimeters long and are brown or dark gray.

The name moth flies comes from Psychodidae’s disproportionately long, wide wings that resemble moth wings. However, drain flies do not use these wings to fly long distances. 

Instead, they appear to hop or jump short distances midair. You might also notice a drain fly’s long antennae with which they feel their way in the dark.

Drain flies typically feed on decaying organic matter, such as human or animal feces, rotting food, or other bacteria.

These little bugs join fungus gnats and fruit flies to form the group known as “gnats.” Here, you can learn how to effectively eliminate common gnats from your home and plants.

(Do you know how to correctly differentiate between drain flies and fruit flies? We explain the differences in this article.)

Drain flies breed at an efficient rate, with one female able to produce up to 300 babies in 48 hours.

Their lifespan is short, however, with a drain fly rarely living longer than 24 days.

This short lifespan and quick breeding makes it important to eliminate drain fly larvae as well as the adults.

Larvae can be easily eliminated by thoroughly cleaning and perhaps treating the pipes that are housing them.

However, after treatment, you might still notice some adults that weren’t in the pipes at the time of treatment searching for a new home and breeding ground.

In this case, traps may be necessary to eliminate the few remaining stragglers. We show you the best traps for adult drain flies here.

Can Drain Flies Come From the Toilet?

Drain flies make their homes and breed anywhere that has plenty of moisture and decaying organic material. This includes drains of tubs, showers, and sinks. 

Even sump pumps can become the source of an infestation. (Here, we show you how to deal with this problem.)

They are also commonly found outdoors near standing water or open sewage.

Head over to our article “What Causes Drain Flies” for a more in-depth look at what attracts them so you can eliminate everything that is luring them in.

Because of this, you might find drain flies near your toilet. Toilets are full of standing water and often contain remnants of sewage. 

However, there is often too much water and not enough organic matter to attract drain flies to the tank or bowl of the toilet.

Unless a toilet contains a large amount of organic material or hasn’t been flushed in several months, the most common place for a drain fly to be in a toilet is the closet flange.

The closet flange is the area of the plumbing where the toilet connects to the pipe.

To get to it, you must disconnect the toilet from its bolts and lift it away from its setting.

If there are drain flies coming from the closet flange, it might be because the toilet is not snug with the floor, allowing them to fly underneath it.

This can occur if the toilet has become loose or if the floor beneath the toilet has warped.

Don’t miss out on important prevention techniques, elimination methods, and recommended products for dealing with drain flies. Check out our entire lineup of drain fly articles here.

How to Eliminate Drain Flies in the Toilet

If you are sure that the drain flies are coming from the toilet, the first step is to determine which part of the toilet they are coming from. 

In our article “How To Get Rid of Drain Flies” you’ll find effective elimination options for both larvae and adults.

The solutions provided will indeed take care of the problem, but with toilets, the source of the drain flies is often less accessible and will require additional steps.

Water Tank

When you lift the lid from the back of the toilet, do drain flies fly out? Do you notice larvae in the tank?

If so, you need to clean out the tank thoroughly to remove the things that attract the bugs.

Turn off the shutoff valve at the back of the toilet. Usually, the shutoff valve is a metal oval attached to a hose that goes into the toilet tank.

This will make it so that no water can enter the tank so you can empty it. 

Once the water is shut off, flush the toilet. The water will disappear from the tank, into the bowl, and down the drain. 

If there is still water in the tank, pull on the chain in the tank to lift the flapper until all the water disappears.

When the tank is empty, dry it out with a towel or washcloth. Look carefully for larvae and scrape them away with a paint scraper or sponge. 

Use a mild soap and warm water on any area that has mold or mildew. This is what attracts the drain flies. 

Once you are sure that the tank is clean, you can use an insect growth regulator. We recommend ZOECON Gentrol Insect Growth Regulator for its effectiveness and ease of use.

Spray the product all around the toilet tank. This will stunt the growth of any larvae that you have missed, as well as any that are laid after the application. 

After letting the IGR dry, turn the water back on and allow the tank to fill itself. Flush the toilet several times to rinse the tank.

Toilet Bowl

If you haven’t flushed the toilet for several months, the combination of rotting bacteria and stagnant water can make it attractive to drain flies. 

To get rid of the gnats, clean the toilet well using a scrub brush and a toilet bowl cleaner, like this one with bleach

Similarly to the tank, the goal is to get rid of any larvae before they hatch.

Simply running water will not eliminate all of them, since they are adhesive enough to stick to the sides and rims of the bowl. 

However, using the toilet brush should be enough to unstick them. 

Likewise, the cleaner should remove all the organic matter in the toilet, taking away the food that attracts the adult drain flies and nourishes the larvae.

Closet Flange

Accessing the closet flange is a somewhat complex task that could have expensive repercussions if done incorrectly. 

If you are not confident in your ability to take the toilet off without breaking it or to reattach it without causing leaks, then do not attempt this project.

Call a professional plumber instead.

  1. First, empty the water from the toilet by turning the water off (as described above). Flush the toilet until no water remains in the tank or the bowl. 
  2. Then, unscrew the bolts holding the tank onto the bowl. There should be one on each side of the tank at the back of the bowl.
  3. Place the tank aside, and unscrew the bowl via the bolts on the floor. 
  4. Lift it up and away and set it aside, being careful not to pull the water hose out of the wall. 

Now you have access to the closet flange, which is a wax gasket held on by two bolts. 

Clean the flange thoroughly, removing it if necessary. The goal is to remove mold or any other substance that might attract drain flies. 

Make sure to use a mild soap so that you do not damage the wax seal. Do not use bleach or abrasive cleaners.

Use a paint stick or scraper to scrape away any film or larvae you can reach. 

Then, pour a half-gallon of boiling water down the pipe. The extreme heat should be enough to kill any larvae on contact. 

If the problem is extreme, add a half cup of white vinegar to the boiling water. The vinegar is powerful enough to kill the larvae without damaging your pipes.

If this doesn’t work, or if you want to ensure that you kill the bugs quickly, try Natural Armor Fruit and Drain Fly Killer.

The thick gel thoroughly coats the insides of your pipes, effectively killing adults, eggs, and larvae.

Made with noncorrosive ingredients, this all-natural gel can be used without fear of damaging pipes or septic systems. Great for long-lasting results.

Fruit Fly & Drain Fly Killer - Simple Commercial Drain Gel Treatment – Eliminates Gross Fruit Flies, Drain Flies, Sewer Flies & Gnat Infestations From Any Drain. Fast & Easy - 1 Gallon (128 Ounces)

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Once you are satisfied that the flange and pipes are as clean as possible, reinstall the toilet in reverse order.

Make sure to line it up correctly so that the pipe fits over the flange cleanly. 

Turn the water back on and flush the toilet several times to ensure there are no leaks.

Conclusion

There might be drain flies coming from your toilet, but they are more likely to come from your sink, tub, or shower drain. 

If they come from the toilet, the most likely culprit is the closet flange, which requires removing the toilet to access. 

Carefully remove the toilet and clean the flange thoroughly.

Pour diluted vinegar and hot water down the pipe to kill the larvae, or use a pipe-safe pesticide that coats the inside of the pipes to kill the young drain flies.

 

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