Getting Rid of Drain Flies: Complete Guide

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Tools, & Tips for DIY Solutions

So you want the ultimate drain fly killer.

Many websites touting “organic” methods do not understand the actual source of infestation.

The good news is that drain flies do not bite. They are a nuisance and can make your home or apartment look unsanitary. We know that is not the case.

Vinicius Rodrigues, PhD

Reviewed by Vinicius Rodrigues, PhD, Entomology

Vinicius is highly experienced in Ecological Simulations, Quantitative Ecology, Community Ecology, Ecological Interactions and Population Dynamics.

what are drain flies

Drain Flies Defined

Drain flies, or sewer flies, are small gnats usually found in bathrooms and kitchens. They tend to be black or brown, and spend most of their time perched on walls or ceilings. Eradicating these insects can be difficult because they breed very quicky and in hard to find areas.

Identification of Psychodinae (Drain Flies)

A very brief lesson in entomology: Psychodinae are the nominate subfamily of moth flies. These are better known as drain flies.

This basically means that multiple genera, or types, of these flies exist. So, if the pictures on this page or across the web don’t exactly match what you see, have no fear. The basic approach to identification and treatment remains the same.

Fly Species Chart

These flies prefer damp habitats, and the larvae primarily live and remain in water.

Phylum: Arthropoda
Order: Diptera
Family: Psychodidae
Common name: Drain fly
sewer fly image

It seem that almost out of nowhere, your home is overrun with these little black flies.

At first, it may seem like a one-off issue. But killing them does not stop the onslaught!

First, we need to make sure you are not confusing them with fungus gnats or fruit flies.

The following are tips to help you identify drain flies:

  • Adult flies are somewhat small and measure about ⅕ to ⅙ inch long.
  • They appear dark, gray or brown in color.
  • Wings covered in fuzzy hair.
  • Adult flies may have ovoid wings wider than their body.
  • At rest, wings appear heart shaped, or roof shaped.
  • Some species can include flies that look like moths.
  • They fly in short, jerky lines (or "hops").
  • Antenna are longer and contain segmented sections


drain fly larva and pupa


Depending on the environment and species, female flies will lay anywhere from 30 to 100 eggs in the material buildup in sewers, sinks and drains. In roughly 32 to 72 hours, the eggs hatch.


The larval stage follows, and lasts between one and three weeks. Larva appear in the area of infestation during this phase. Some refer to these larvae as drain fly worms.


In the last developmental phase, larvae grow into pupa. This is the last stage before they become an adult fly. They spend about one week in this phase.


Fully mature adult imago flies will live for about 14 days. Killing adults may not solve the issue if eggs and larva still exist in the infestation area.

Drain Fly Vs Fruit Fly

Fruit flies tend to stay in groups and cluster around areas of rotting fruit or garbage.

Unlike drain flies, fruit flies hover in the air, have very small antenna, and lack the distinct heart shaped ovoid wings.

drain fly vs fruit fly

Female fruit flies tend to lay their eggs on the surface of or inside overripe fruit.

Drain flies breed in aqueous environments. Adult females lay eggs on the buildup inside pipes, drains or standing water. They will not lay eggs in humans - something some individuals are worried about.

A distinctive giveaway of the fruit fly is also the red eyes or striped abdomen (which it has in general).

Do They Bite or Harm Humans?

No. Drain flies do not bite and are not known to transmit diseases to humans.

In some instances, drain fly activity and biomaterial can trigger asthma.

In the majority of cases, drain fly infestations are a simple annoyance. There is not need to worry about health ramifications.

where do drain flies come from

Where do Drain Flies Come From?

They live in drains, sewers, septic systems and shallow water with scum buildup.

Fly larvae, which are aqueous, grow and feed on the organic matter. These flies are typically seen in bathrooms and kitchens.

It is easy to assume they swim through pipes, but that is probably not the case. Drain flies usually make their way into a home from the outdoors or basement.

David Shetlar of OSU's Entomology department wrote that drain fly eggs hatch at a preferred temperature of 70°F. However, this can change depending on the species. Most like mild temperatures between 70-77°F and median to high humidity levels.

Expect to see these pests in warmer weather, such as summer and spring.

Preferred Habitats

Drain flies, like their name suggests, are most commonly found in pipes and drains. However, they are also in other areas such as:

  • Sink drains
  • Infrequently used toilets or tanks
  • Unwashed garbage disposals
  • Windows and walls near drains
  • The sides of showers
  • Under shower pans
  • Unused sinks
  • Under the sink with a leaky pipe
  • Garage floor drains & basements
  • Loose tiles with moisture present (bathrooms)
  • Sump pump pits

Outside or Around Your Home:

  • Sewage contaminated soil (broken or roots in sewer lines)
  • Septic tanks
  • Damaged septic line
  • Garbage areas
  • Compost piles
  • Rotting logs or tree cavities
  • Bird baths

Standing Water

  • Shallow, polluted ponds
  • Rain barrels
  • Compost with high-moisture organic material
removing flies from house

Get Rid of Drain Flies

Here’s how to get rid of organic material where these flies breed:

  1. Find the drain or location where they are breeding.
  2. If in pipes or drains, manually remove buildup with a pipe brush.
  3. Flush/remove any standing water or breeding material from the site.
  4. Follow with an enzymatic or bacterial drain cleaner.
  5. Eliminate adult flies with an aerosol or swatter.
  6. Use Gentrol IGR to stop the lifecycle.
  7. Flush the drain or sink regularly with water.

Testing Drains for Infestation

If you suspect flies are coming up from a drain, place a piece of tape over the drain. If you find flies stuck to the underside of the tape after a period of time, the drain is likely a source.

Make sure to test all drain or sinks in the vicinity, as there may be more than one breeding ground.

You may be able to spot larva near the surface by using a strong flashlight in larger floor drains.

Eliminate Fly Food Sources

As mentioned above, organic material in your pipes and drains attracts drain flies. It acts as the larva food source.

And thus, if you remove the organic material, you take away their food source.


Clean in and around sinks, drains, and pipes. Scrub drains with a metal pipe brush. Make sure to use a long and stiff brush.

Push the brush through the pipe to dislodge the accumulated material.

Look for a pipe brush set that has a wide range of brush lengths and widths. This will make cleaning pipe walls much easier.

Pouring a pot of hot water will help loosen the material buildup.

Remove standing water in soggy areas around house plants, refrigerator drain pan, and wet lint in the laundry area.

Sump Pits & Drainage Basins

Sump pump pits present a unique challenge. Their inherent design provides an ideal breeding environment. Make sure the pump is working so you can cycle out water often.

If the pump float switch does not trigger a cycle, manually activate the pump at least once each month. This will prevent the water from getting stale.

You can also throw in a few Bio Bullet or Green Gobbler Bio-Flow strips. We found both to be effective at reducing the natural buildup in the pit.

Note that they might cause some residue to appear on your pump.

Lastly, consider a Gentrol spray, which is approved for use in drainage areas. Don’t forget to keep that pit sealed.


Eliminate all standing water near and far from your house whenever possible. Clean your air conditioners, garbage bins, and birdbaths.

Look around your property for any rotting firewood or logs. If you have any potted plants near your home, check the soil and water saucer for activity. Some types of plants might also be more prone to attract flies.

Interrupting the Fly Lifecycle

To stop drain flies from multiplying, you have to eliminate larvae and adult flies once and for all.

Drain fly breeding sources are just above the waterline.

Here’s how to get rid of organic material where these flies breed.

  1. Clean the drain’s exterior. Moisten the drain by pouring 2 to 4 liters of warm water.
  2. Clean the sides of the pipe with a metal pipe brush. You can also use a drain snake to pull out the organic matter.
  3. Make sure to scrub under the rubber drain skirt - an area where buildup goes unnoticed!
  4. Coat the sides of the pipe with a drain cleaning gel. A drain gel is an effective drain fly killer. It has a formulation specifically designed in removing organic matter from the drain.

Many homeowners believe that pouring hot or boiling water down the drain is enough. This is not the case.

Drain fly larvae survive in extreme temperatures, so this method is not recommend. The level of heat needed to kill larva and eggs will also put your pipes at risk

Additionally, the boiling water can harm plumbing infrastructure or crack surfaces.

Most older homes cannot handle temps above 150°F. Keep this in mind if you are using Drano or Liquid Plumbr to clear blockages.

Wait for a few hours before flushing down the drain with plenty of water. You can use a cup plunger to effectively take out all the remaining organic material.

RV Gray & Black Water Tank Infestations

Nothing puts a damped on a sweet vacation or travel like flies covering your RV bathroom walls. This is a common occurrence that is easy to avoid, but a bit annoying to treat.

  1. Make sure you close the sewer hookup valves to prevent flies from finding their way into your tanks from below.
  2. If you suspect an infestation, flush and clean your tanks using these methods.

Keeping a clean tank is a very good practice, as is something you should consider even if you never see a drain fly in your life!

Eliminate the Eggs, Larva and Adult Flies

Drain fly larva are tough. They are generally not easy to spot unless they travel to the waterline. They tend to remain in the organic buildup inside of pipes and drains. This makes removal a bit more tedious.

Adult female flies leave their eggs just above the water line. Bleach and Drano are the most common chemicals homeowners use to try and kill flies.

However, they are not the best treatment method for larva or eggs. Yes, they can kill larva and pupa. But, the fly breeding ground - the gelatinous buildup - will likely remain.

Using Bleach

While bleach can kill drain fly larvae, it’s not enough to get the job done.

Unlike drain gels, bleach doesn't stick to the sides of drains and pipes. It may may pass down the drain with little to no effect.

Normally, there is not enough resting time for it to penetrate the thick organic material where the larvae and eggs hide.

Bleach has corrosive properties and can damage older pipes if used in an undiluted state.

There are also issues with using bleach in combination with other liquids. Here are some of the dangerous combinations to avoid:

  • Bleach with Ammonia can produce toxic chloramine vapors.
  • Bleach and rubbing alcohol produce chloroform which we all know is harmful to humans.
  • Mixing bleach with vinegar results in toxic chlorine gas.

In conclusion, using bleach as a drain fly killer is not recommended. If you need a solution fast, don’t waste your time or money on bleach.

Will Drano or Drain Cleaner Work?

Yes, it can.

Drano Gel gel for flies

Drano drain cleaner has the ability to clear clogs in pipes, but does it work for drain or phorid fly infestations?

It contains chemical properties that will burn and corrode tissue with prolonged contact.

The main ingredients are sodium hydroxide, sodium hydroxide and sodium silicate. (A corrosion inhibitor for pipes.)

Many licensed plumbing professionals believe that Drano causes issues with prolonged use.

This contradicts S. C. Johnson & Son's lab tests which ensures that their product does not harm plumbing systems when used properly.

Drano may not clear up the primary source of infestation. In a few days or weeks, flies could be reappearing once again even though you killed off many adult flies.

Aerosol Spray

Chemical sprays are great at killing adult drain flies. Keep in mind that they may not be suitable in areas like your kitchen and dining room.

Sprays can work wonders in fly infested bathrooms and basements.

Liquid Dish Soap Mix

Here’s how to make an improvised dish soap spray.

  • Add 5 to 7 drops of dish soap into an empty spray bottle.
  • Add 2 cups of warm water.
  • Shake the mixture before spraying adult flies.

Flytrap or Tape

A non-toxic, somewhat old school solution is to use fly paper. This tape draws flies to it with an appealing scent. When they land on the tape, they will stick and be unable to move.

fly product review

Drain Gel & Products Overview

InVade Bio Drain

InVade Bio Foam or gel is a highly concentrated micobial drain gel. The advanced probiotic and microbial formula to eats away organic buildup.

This particular gel also contains citrus oil which emparts a pleasant scent. A gallon jug contains up to 33 treatments.

Green Gobbler Fly Killer

The Green Gobbler Fly Killer Gel contains citronella oil. The smell of citronella is known to repel certain flying insects.

Try their Enzyme Drain Cleaner which does the exact same thing, but for about $10 less.

Gentrol IGR

Gentrol IGR is an aerosol spray that acts as an insect growth regulator (IGR).

An IGR works by interrupting the normal development of insects, drain flies included.

Gentrol IGR is a must for treating drain fly infestations since it stops the life cycle.

Forid Drain Gel

Florid Drain Fly Gel works like any other drain gels. However, this one is a concentrated organic drain cleaning gel and costs more than its competitors.

Florid Drain is marketed as a high-end product, but you will likely need more than one bottle for heavy infestations.

A unique feature is the built-in measuring cup.

when to call a plumber

When to Call a Plumber or Exterminator

In some cases, homeowners, commercial property managers or restaurant owners need expert assistance.

A fly infestation left untreated will get worse, and may spread to other areas of the home or building.

In public institutions, it is not uncommon to see the occasional drain fly perched on a wall. This typically goes unnoticed by visitors and staff until it is too late.
When to call professional help:

  • You cannot locate where the flies are breeding.
  • There is a deep blockage in the drain that needs removing.
  • Nothing seems to work, flies continue to reappear 4-6 weeks after treatment.
  • There are leaks in your walls or pipes that need fixing.
  • You are a property manager in need of a quick solution that will succeed.
  • You are a homeowner looking to sell.
  • The smell of sewage is present in and around the property.

In these cases, calling an exterminator or plumber is the right approach. Typically, exterminators will treat drain fly problems in a similar manner as our DIY approach.

They may not be equipped to open pipes for inspection and manual cleaning.

Most typically treat drains with a gel, or help find infested drains using a fly tape or sticky board method.

In our research, we found many plumbers who were well versed in dealing with fly infestations.

In many cases, they will snake the line to remove blockages, and even open pipes to clean out p-traps as necessary.

Sewer Line Break

If you suspect a break in your main sewer line, a plumber can validate the issue with a special camera.

If there is a break beneath the slab of your property, it might be wise to include both a plumber and exterminator to combine their expertise.

Breaking the floor and removing contaminated soil is a huge job. It pays to spend a little bit extra to ensure the process is done right. This also helps avoid reinfestation after a new floor is poured.

Difficult Blockages

At times, no amount of drain cleaner or snaking will work.

In these cases, a call to you local plumber might save you many headaches and wasted dollars.

Have them check your lines to ensure they are clear. This could help, particularly in showers, where a slow and steady may lead to infestation.

When Your Tenants Are Unhappy

Real estate owners and landlords know how important it is to keep tenants happy.

Likewise, as a renter, nothing is bothersome as a landlord who does not care. In this case, it might be wise to call out a pro immediately to fix the issue asap.

drain fly removal guide infographic


Identifying and treating drain flies with the proper methods is the only way to get rid of them for good.

Whether you own a home, commercial property or restaurant, manual drain cleaning and drain gels can work for you.

Always make sure to first identify the correct drain or source. Then follow with a committed treatment and sanitation program to improve long-term prevention.