12 Ways To Get Rid of Drain Flies (Natural & Chemical Methods)

Are flies buzzing around your sink or floor drain?

These pesky buggers are known as drain flies, and they literally breed and feed on the gunk inside drain pipes.

Even though drain flies are similar in size to fruit flies, they are a distinct species and actually look moth-like with furry wings and bodies.

In this guide, we’ll go over…

• Natural methods to kill drain flies like boiling water and vinegar
• Chemical strategies such as drain cleaners
• Physical tips such as sealing drains and even using wet/dry vacuums

Let’s get started!

What To Know Before Getting Rid of Drain Flies

• Drain flies are about the same size as fruit flies but are a distinct species with a furry moth-like appearance
• Drain flies are also known as sewer gnats, moth flies, sewage flies, and drain gnats
• They do not bite or transmit disease to humans but are unsanitary
• Adult sewer gnats lay eggs inside of drains, especially in the P-trap section (most common)
• The life cycle of drain flies is short at about 2-3 weeks and can multiply quickly
• Adult moth flies do not live inside the drain but usually stay close to it
• The eggs and larvae live inside the drain until adulthood, feeding on the slime
• Egg to larvae state is 1-2 days, larval stage is 10-15 days, pupal stage is 1-2 days.

Strategy #1: Boiling Water

Boiling water is a simple and effective natural method to eliminate drain flies.

During the larvae and egg stage of sewer flies, their soft bodies are susceptible to scalding water, and most will be killed on contact.

This method works because the hot water can disrupt the life cycle of the insects. Sewer gnats only live for a few weeks, so a sudden disruption to their breeding ground can knock out the infestation.

The hot water also helps to dissolve the organic sludge buildup on the P-trap surface of drains.

However, the boiling water may not fully penetrate the biofilm inside the drain, so it’s best to combine this method with a drain cleaner, vinegar and baking soda mix, or a manual drain brush if it’s a bad infestation.

Boil 1/4 to 1/2 gallon of water, and slowly pour it down the drain. I recommend doing this daily until the drain flies are fully eradicated. You can also do it about once a week for drain maintenance.

6 Steps To Using Boiling Water

1. Clear the drain of any visible food or debris
2. Boil 1/4 to 1/2 gallon of water in a pot or kettle
3. Slowly pour half of the water into the drain
4. Wait about a minute for the hot water to settle in the drain
5. Pour the remaining water
6. Repeat daily or once a week.

Strategy #2: Vinegar and Baking Soda

Vinegar and baking soda is an inexpensive and non-toxic way to kill pesky drain flies.

Baking soda is a mild alkaline powder (sodium bicarbonate) which reacts with the vinegar (acetic acid) to form a fizzy reaction. This foamy solution destroys the organic biofilm that lines your P-trap that sewer gnats use to feed and reproduce.

And due to its slightly abrasive nature, vinegar and soda will also directly kill the larvae and eggs living in the drain. The vinegar and baking soda also help neutralize odors which stops new drain gnats from being attracted to the area.

This method is much milder than commercial cleaners so repeated or daily use may be required — each time it dissolves the biofilm a bit more. For very thick biofilms or severe infestations, it is best to combine this strategy with a chemical drain cleaner or manual brushing.

This method releases a small amount of carbon dioxide so I recommend keeping the room ventilated or cracking open a window.

5 Steps To Using Vinegar and Baking Soda

1. Pour a 1/2 cup of baking soda into the drain.
2. Slowly pour 1 cup of white vinegar into the drain, allowing it to mix with the baking soda.
3. Wait 15-30 minutes for the solution to sit in the drain.
4. Once fizzing stops, flush hot water down the drain for 10-15 seconds.
5. Repeat daily until no more drain flies are seen.

Strategy #3: Flexible Drain Brush

Flexible drain brushes, with their long reach and stiff bristles, effectively clean deep within your drain’s P-trap.

These inexpensive brushes will mechanically remove the grimy biofilm that drain fly larvae and eggs live on — stripping it instantly which chemical cleaners cannot do.

This physical method is perfect for thick biofilms that may be resistant to natural or chemical cleaners. You can also combine drain brush cleaning with boiling water or vinegar-soda for an even stronger cleaning.

It’s best to find a drain brush that correctly fits the diameter of your drain pipe. Measure your P-trap size first if possible. Also, try to estimate the length of drain brush that you need to get all of the P-trap which is where most of the sewer gnat activity is located.

The side benefit of this strategy is that it should improve drain flow, making your fixture work better.

7 Steps To Using Drain Pipe Brush

1. Choose a drain pipe cleaner, ideally 1.5 to 2 inches in size to match most sink drain pipes.
2. Remove stopper or drain pipe cover if needed.
3. Insert brush into drain and push it down into the P-trap.
4. Push down and pull up several times, scraping the walls of the P-trap.
5. Remove brush and rinse it off.
6. Turn on hot water and allow it to drain for 15-20 seconds.
7. Repeat as needed.

Strategy #4: Gel Drain Cleaner

Gel drain cleaners are a fast, chemical-based solution to eliminate drain flies in your kitchen or bathroom. The gel is thick and sticky so it will cling to the inner walls of the drain pipe.

The chemical gel doesn’t kill sewage flies directly, but it dissolves the biofilm in the drain made of grease, hair, and food debris.

This organic film is what that makes up the breeding ground of sewer gnats. Dissolving this sludge disrupts the reproductive cycle, and prevents new eggs from being laid inside.

It’s best to pour gel drain cleaner in the evening so it can work undisturbed through the night. In the morning, after several hours, turn on the hot water and thoroughly flush out the cleaner and dissolved gunk.

You can combine this method with a flexible drain brush for extra thoroughness in removing sludge.

7 Steps To Using Gel Drain Cleaner

1. Prepare the drain by removing any visible debris (or cover if needed).
2. Follow the product instructions and slowly pour the gel into the drain (typically 8-16 ounces or half the bottle).
3. Ventilate the area by cracking open a window or turning on an exhaust fan.
4. Leave the bottle by the sink to remind occupants to avoid using it.
5. Allow the drain cleaner to sit for several hours or preferably overnight.
6. Flush the gel with hot water for a few minutes to clear out the sludge.
7. Reapply every day or two if drain flies persist.

Strategy #5: Bleach

Bleach is a highly effective method for killing drain flies, but it must be used with caution.

It is a strong disinfectant that will break down the organic sludge that clings to the drain pipe walls.

Bleach will also kill some bacteria and microbial growth as well as some drain gnats with direct contact.

The strategy is to dilute bleach with water at a 1:10 ratio and pour it into the drain. Allow the diluted bleach to sit overnight for maximum effectiveness.

It’s essential to avoid mixing other cleaners like ammonia or vinegar with bleach because it can react and release toxic gases. And I don’t recommend using bleach if you have a septic system since it can harm beneficial bacteria that it relies on.

5 Steps To Using Bleach

1. Crack open a window or turn on an exhaust fan to ventilate the area.
2. Pour 1/2 cup bleach or diluted bleach (1:5 or 1:10 ratio of bleach to water) into the drain.
3. Allow the bleach to sit for at least 15-30 minutes to break down the sludge and to kill larvae.
4. Flush with hot water for a few minutes to clear out debris and dead larvae/eggs.
5. Repeat daily as needed.

Strategy #6: Enzyme-Based Drain Cleaner

Enzyme drain cleaners work similarly to chemical drain cleaners but are non-toxic and safe for septic systems.

Instead of using chemicals to kill the biofilm, it relies on enzymes that eat the microbial gunk and grime. It won’t kill drain flies directly but it consumes the organic slime that drain flies use to breed — indirectly reducing their population.

Ideally, you want to leave the enzyme drain cleaner in your sink, tub, or floor drain for at least a couple hours but overnight is best if possible.

I recommend using the drain cleaner each day until the drain gnat population is destroyed.

Enzymatic drain cleaners are also great for periodic maintenance to keep your P-traps free of gunk, reduce foul odors, and improve water flow.

6 Steps To Using An Enzyme-Based Drain Cleaner

1. Pick a drain cleaner that uses enzymes instead of chemicals.
2. Prepare the drain by removing any visible debris and drain covers that may get in the way.
3. Follow the instructions and pour the drain cleaner into the sink or drain.
4. Allow the solution to sit in the drain for at least a few hours but preferably overnight.
5. Flush with hot water for 1-2 minutes.
6. Repeat use daily until drain fly population collapses.

Strategy #7: Wet/Dry Vacuuming The Drain

If you own (or can rent) a wet/dry vacuum, it can be a chemical-free way to mechanically remove sludge from the drain. Wet/dry vacuums are generally safe for all plumbing types including PVC and metal.

The sucking force of a wet/dry vacuum can pull out some of the slime, larvae, eggs, and biofilm that is the reproductive home of drain flies.

It’s essential to create a strong seal where you insert the vacuum hose, and to use an attachment size that matches the drain opening (or slightly smaller). You can use a rag or cloth around the vacuum attachment to create a strong seal.

Don’t forget to set the wet/dry vacuum to wet mode so you don’t damage the vacuum.

While a wet/dry vacuum won’t totally kill the drain moth fly infestation, if you combine it with a drain cleaner, boiling water, or other chemical method — it can accelerate the collapse of the sewage fly population.

7 Steps To Using A Wet/Dry Vacuum

1. Set vacuum to ‘wet mode’ and remove internal filter (if not rated for wet use).
2. Choose a vacuum attachment that will fit snugly into drain hole. Wrap the attachment in a rag or duct tape for a tight seal.
3. Remove any drain cover or sink stopper that will get in the way.
4. Insert nozzle and press it in firmly for a strong seal.
5. Turn on vacuum and let it run for 1-2 minutes.
6. Turn off vacuum and check collection tank for debris (and see how effective it was).
7. Repeat every day or as needed.

Strategy #8: Clean Or Replace Drain Covers

The covers on floor or bathtub drains can become dirty, corroded, and full of slime that is highly attractive to drain flies. Also, sink strainers and sink stoppers can accumulate slime that becomes the breeding ground for drain gnats.

I recommend removing any existing drain cover if there is an infestation and to thoroughly clean it with water and dish soap.

For very dirty covers, you can let it soak in a diluted bleach solution (10:1 water to bleach) for 10 minutes, and then scrub it with a brush. If the drain cover is highly corroded, replacement is recommended.

In addition, you may want to purchase a fine-mesh drain cover to prevent sewage flies from entering or exiting the drain whatsoever.

Cleaning, replacing, or adding a fine-mesh cover is a good way to kill drain moth flies for minor infestations. However, I still recommend pairing this strategy with a drain cleaner, boiling water, or some other strategy to kill the biofilm in the drain itself.

6 Steps To Cleaning Or Replacing Drain Cover

1. Remove the drain cover using a screwdriver or flathead if needed
2. Scrub the cover with a brush, hot water, and dish soap. You can soak it in a diluted bleach water solution if needed.
3. Using the same brush, clean around the drain opening.
4. Rinse off and dry the drain cover.
5. Re-install the drain cover (or install new one if badly corroded).
6. OPTIONAL: Place a fine-mesh screen over the drain cover to prevent flies entering drain.

Strategy #9: Apple Cider Vinegar Fly Traps

Apple cider vinegar traps effectively capture adult fruit flies, which reduces egg-laying inside the drain. The smell of vinegar mimics the odors given off by decaying food and naturally attracts adult drain flies.

The idea is to put out apple cider vinegar (or white vinegar though less effective) in a container along with a drop of dish soap. The dish soap helps to break the surface tension so the drain gnats get stuck in the vinegar when they land on it.

You can also cover the container with plastic wrap, and poke it with a few holes to ensure the sewage gnats can’t escape.

This strategy is best coupled with other cleaning solutions since it won’t affect the drain pipe itself and the egg/larvae population already living in the drain.

I recommend adding vinegar daily or as needed and place it as close as possible to the infested drain.

6 Steps To Using Apple Cider Vinegar

1. Pour about half a cup of apple cider vinegar into a cup or bowl.
2. Put a couple drops of dish soap into the vinegar and stir.
3. Cover the container with plastic wrap, and poke several holes with a toothpick or fork.
4. Place the trap near the infested drain, and leave it overnight.
5. Replenish and clean the container as needed for at least 3-5 days.
6. Combine vinegar trap with drain cleaner or brush cleaning.

Strategy #10: UV Light Traps

UV light traps for flying insects can be a clean and easy way to kill adult drain flies. While UV light traps don’t kill larvae or clean the drain, it can stop or reduce new eggs from being laid inside the drain.

Drain gnats are naturally attracted to ultraviolet light, and when they land on it, they get stuck in the glue or get zapped by electricity.

The best part about UV light traps is that they are easy to use by plugging into a wall outlet (or battery powered) and there is little or no mess.

UV light traps are an effective treatment especially when used in combination with a drain cleaner.

It’s essential to leave the UV light trap away from other competing sources of light that the flies may be attracted to. When you go to sleep, make sure all lights are off in the area of the trap.

6 Steps To Using UV Light Traps

1. Plug in or turn on the UV light trap and place it near the infested drain.
2. Keep the UV light trap on in the evening or overnight.
3. Make sure the room is as dark as possible.
4. Clean the collection tray of dead drain flies everyday.
5. Use the UV light trap nightly until the adult drain fly population is dead.
6. Combine with drain cleaning to kill the larvae and eggs.

Strategy #11: Fix Leaks And Reduce Moisture

For long term prevention of drain flies, it is critical to stop all sources of leaks and moisture in your bathrooms, kitchens, and utility rooms.

I recommend using a flashlight to check for leaks, pooling water, or signs of corrosion.

Sewer flies need moisture and an organic biofilm to breed and survive with their extremely short life cycles of a few weeks. It’s best to control moisture alongside drain cleaning to stop drain gnats in their tracks.

You can also use fans and dehumidifiers to dry out any bathrooms that have excess humidity.

Keeping these areas dry that are prone to sewer flies helps to manage and kill them.

5 Steps To Reducing Moisture

1. Use a flashlight and check for leaks around sinks, drains, and along pipes.
2. Use a wrench to tighten fittings, nuts, and drain connections if leaking.
3. Clean up standing water and moisture with a rag.
4. Improve ventilation of area with standing fan, exhaust fan, opening a window, or dehumidifier.
5. Monitor area over next few days to see if moisture has decreased.

Strategy #12: Sealing Unused And Dry Drains

Drain flies commonly infest drains from unused bathrooms, utility sinks, and floor drains.

The reason for this is that unused drains dry out at the P-trap. This plumbing bend is supposed to hold water inside to create an air seal — and to prevent sewer gases from leaking into the home.

But if the P-trap isn’t used, evaporation will eventually dry out the P-trap, which allows drain gnats to nest and breed inside the drain undisturbed.

Simply adding water to an unused floor drain or briefly turning on a sink can help stop sewer flies from taking root. One common household trick is to add a bit of mineral spirits to the drain which floats on top of the water and slows down the rate of evaporation.

If you have an unused floor drain, sink, or bath tub, you can also totally seal the drain with duct tape, a solid drain cover, or a rubber plug.

Final Thoughts On Drain Gnat Pest Control

Drain fly infestations can be an annoying problem. Sewer gnats can make your your sink or drain unsanitary and repulsive.

Fortunately, there are numerous methods to control and destroy drain gnat colonies.

The best approach is usually a combination of methods such as boiling water, drain cleaner, vinegar traps, or just sealing an unused drain. It’s important to be persistent and to keep your kitchen, bathroom, or utility room free of moisture and plumbing leaks as well.

You may want to install new drain covers with fine-mesh screens to keep out drain flies permanently.

I hope you enjoyed this guide by TimberSill, please share your experience below with drain flies or ask me a question!