How to Get Rid of Drain Flies and Keep Them Away

To get rid of drain flies, you have to clean the breeding site, not just swat the adults. Those fuzzy little flies hovering near your sink are living off a layer of gelatinous organic gunk, called biofilm, that coats the inside of your pipes, and until you physically scrub that film out, more flies keep hatching. The fastest reliable fix is to confirm which drain is breeding them with a simple tape test, scrub the pipe with a stiff brush, and then treat it with an enzyme drain cleaner, so this guide walks through exactly how to get rid of drain flies and keep them from coming back.

Everything below is organized the way an actual eradication goes: identify, confirm the source, kill what is in the pipe, verify, and prevent. Skip the first steps and you will be back here in two weeks.

What are drain flies, and what causes them?

Drain flies, also called moth flies, filter flies, or sewer gnats, are tiny insects roughly 1.5 to 5 mm long with fuzzy, moth-like bodies and broad wings they hold roof-like over their backs. They are weak fliers, so you usually see them resting on walls, mirrors, or the sink basin near where they emerged rather than zipping around a fruit bowl.

Here is the part most people miss, and it is the single most important idea in this article: drain flies are not a cleanliness problem on your countertops; they are a film problem inside your plumbing. Virginia Tech Extension explains that adult females lay their eggs in the gelatinous, sludgy organic material that accumulates on the sides of drains, overflow pipes, and traps. The larvae live buried in that slime, feeding on the bacteria, hair, soap scum, grease, and food residue packed into it. NC State Extension puts it plainly: drain fly larvae need the bacteria-rich biofilm found in pipes.

So what causes drain flies? A drain that holds a steady supply of moist organic gunk. That is why they show up in:

• Rarely used sinks, floor drains, and basement or utility-room drains where water does not flush the pipe regularly
• Shower and tub drains loaded with hair and soap film
• Kitchen drains and garbage-disposal splash guards caked with food grease
• Overflow holes in sinks, which almost never get cleaned
• Sump pits, floor drains under appliances, and the gaps around a leaking pipe

Iowa State Extension notes that the drain itself is essentially the only effective place to eliminate them, because that is where the breeding material and the larvae are. Kill a cloud of adults with a spray and it feels like progress, but if larvae are still buried in the pipe, the next generation is already on its way.

Drain fly vs fruit fly vs fungus gnat: which pest do you actually have?

Before you spend an evening scrubbing a drain, make sure you are chasing the right insect. The three small flies people confuse indoors breed in completely different places, and the wrong treatment simply will not work. The most reliable way to tell them apart is not size or color, which overlap and vary, but where they breed and how they behave.

A quick field test: if the flies rest flat on the wall beside the sink and barely fly when you wave at them, you are almost certainly dealing with drain flies. If they scatter into the air around your bananas or the recycling bin, those are fruit flies. If a little cloud erupts from a houseplant when you bump the pot, those are fungus gnats feeding on plant roots in the soil. Fruit fly tricks will not touch a drain-fly population, and drain cleaning will not fix a fruit fly problem, so nail the identification first.

Why are there drain flies in my bathroom specifically?

Bathrooms are the number-one drain fly hotspot, and it comes down to what goes down those drains. Shower and tub drains collect hair, sloughed skin, conditioner, and soap scum, all of which congeal into exactly the kind of moist, nutrient-rich film larvae thrive in. Sink overflow holes, that little slot near the top of the basin, are a hidden favorite because water rarely flushes through them and nobody ever brushes them out. Toilets that get infrequent use, like those in a guest bathroom, can also breed flies in the standing water.

Drain flies in a bathroom also point to moisture that lingers. A slow-draining tub, a running toilet, or a small leak at a pipe joint keeps organic matter wet around the clock. In rare cases, flies emerging in a bathroom indicate a cracked or broken sewer pipe or a dry P-trap letting sewer gas and insects up from the line below, which is one reason a persistent infestation that survives thorough cleaning is worth a plumber’s look.

How do I find the breeding drain? The tape test

You cannot clean a drain you have not identified, and homes often have more suspect drains than you would guess: both bathroom sinks, the tub, the shower, the kitchen sink, a laundry drain, a floor drain, a basement drain. The classic, extension-recommended way to pinpoint the source is the tape test, and it costs nothing.

1. Take a strip of clear tape and stretch it loosely across the mouth of a suspect drain, sticky side down.
2. Do not seal the opening completely. Texas A&M Extension stresses this: if the drain is fully covered, there is no airflow and the flies will not try to emerge, giving you a false negative. Leave a gap so air still moves.
3. Leave the tape in place overnight, ideally for a few nights, since flies do not all emerge at once.
4. Check the tape. Adult drain flies stuck to the underside mean that drain is breeding them.

Run the test on every drain at the same time so you can compare. An alternative favored by Ohio State and University of Kentucky entomologists is to invert a clear plastic cup, lightly coated inside with vegetable oil or petroleum jelly, over each drain for several days; emerging adults get stuck to the greased surface. Either way, the goal is the same: find the exact source before you treat, because you may have more than one, and you have to treat them all.

How to get rid of drain flies, step by step

Once you know which drains are breeding flies, work through the steps below in order. The sequence matters: scrubbing first exposes the film so the follow-up treatment can reach the larvae, and treating before scrubbing mostly wastes product on the surface of the gunk.

1. Clear and expose the drain. Remove the stopper, strainer, or drain cover and any pop-up assembly you can take out by hand. Pull out the visible mat of hair and sludge. If the fixture has an overflow hole, remember it, you will clean that too.
2. Loosen the gunk with hot water. Pour a kettle of very hot or boiling water down the drain to soften the grease and film. Virginia Tech notes hot water alone gives only short-term control by killing surface larvae, so treat this as prep, not the cure. (Skip boiling water on fragile PVC traps if you are worried about them, and never pour boiling water into a porcelain fixture it could crack.)
3. Scrub the pipe mechanically. This is the step that actually works. Using a stiff, long-handled drain brush, scrub the inside walls of the drain opening and as far down the pipe as you can reach, removing all the slime and sludge. For deeper runs, feed a drain snake or a metal pipe brush down and work it against the walls. Virginia Tech is explicit that thick, accumulated material requires physical cleaning with a stiff brush, and the sticky-trap test later tells you whether you reached it. Do not forget the overflow hole: run a small bottle brush or pipe cleaner through it.
4. Apply an enzyme or bacterial drain cleaner. After scrubbing, pour in an enzymatic or bacterial drain gel made for this purpose (bio-enzyme drain treatments and foaming drain cleaners are sold for exactly this). These products contain microbes and enzymes that digest the remaining organic film the brush could not reach. They work on contact time, so pour them in at night when no one will run water, and let them sit for several hours or overnight. Do not chase them with bleach, which kills the very bacteria doing the work.
5. Repeat nightly for about a week. The egg-to-adult cycle runs roughly one to a few weeks depending on temperature, and eggs or larvae you missed will still hatch. Re-treating each night for about seven days catches the stragglers so you break the cycle instead of denting it.
6. Treat every suspect drain, not just the obvious one. If the tape test flagged more than one drain, or if you are unsure, clean and treat them all in the same stretch. Missing one breeding drain lets the population rebound across the whole room.
7. Knock down the remaining adults (optional, temporary). The adults you can see will die off on their own within days once breeding stops, but if they bother you, an aerosol labeled for flying insects will drop them. Texas A&M is clear this is cosmetic, it does nothing to the larvae in the pipe, so never treat a spray as the solution.

How to get rid of drain flies naturally

If you would rather avoid commercial chemicals, you can get rid of drain flies naturally, with one honest caveat: the mechanical scrubbing in step 3 above is non-negotiable either way. No natural pour-in dissolves a thick biofilm on its own. With that said, here is the widely used baking soda, salt, and vinegar method, which works as a mild cleaning-and-flush treatment after you have brushed the pipe:

1. Sprinkle about ½ cup baking soda and ½ cup salt into and around the drain opening.
2. Slowly pour in 1 cup of white vinegar. It will fizz; that reaction helps lift loosened residue off the pipe walls.
3. Let it sit for several hours, or overnight for a stubborn drain.
4. Flush with a kettle of boiling water in the morning.
5. Repeat every few days until the flies are gone.

Scale the amounts up proportionally for deep or badly infested pipes. Boiling water on its own, poured down the drain once a day for a week, is another low-tech option that kills surface larvae but will not clear embedded film. Be realistic about the limits here: Terminix notes the baking-soda-and-vinegar approach is not always strong enough to kill every drain fly, and it reaches larvae in the pipe better than adults in the air. Treat natural methods as a solid follow-up to scrubbing, not a replacement for it. One practical warning: if a drain is clogged, do not leave strong mixtures sitting in older or lightweight plastic traps for long, and never combine vinegar-based cleaning with bleach.

How to kill drain flies: what works vs. the myths

Searches for “how to kill drain flies” surface a lot of folk remedies, and some of the most popular ones quietly fail. Here is the honest breakdown.

Why bleach alone usually fails

Pouring bleach down the drain is the most common mistake. It feels decisive, but the drain fly larvae and eggs live embedded in the biofilm clinging to the pipe walls, often below the waterline, and bleach is a thin liquid that rushes straight past that film and down the pipe without soaking into it or stripping it off. The gunk, and the larvae inside it, stays put. Virginia Tech Extension specifically lists pouring bleach down a drain as not recommended because it is not very effective, and extension specialists repeatedly stress that you do not have to pour bleach, you have to remove the material. Bleach can also corrode some pipe metals, and mixing it with ammonia-based cleaners releases toxic gas, so it carries risk without solving the problem.

Why insecticides down the drain are the wrong tool

Virginia Tech is blunt that insecticides should never be poured down a drain to control drain flies. They do not clear the breeding film, they can be hazardous in your plumbing, and they are not labeled for it. Flying-insect aerosols kill visible adults but, again, leave the pipe-dwelling larvae untouched.

Why enzyme and bacterial cleaners beat bleach

Enzymatic and bacterial drain products are built for this exact job. Instead of trying to disinfect a surface, they digest the organic slime where the larvae live, eating away the food source and habitat. Because they rely on living microbes and enzymes working over time, they need contact time (hours, ideally overnight, with no water running) and they must not be mixed with bleach or harsh chemical openers, which kill the bacteria. Paired with a stiff-brush scrub to break up the film first, they address the cause rather than the symptom. Note these are consumer and pest-control recommendations; the mechanism is well supported in that literature even where university publications emphasize the brush above all.

The bottom line: mechanical cleaning is the proven core fix, enzyme or bacterial cleaners are the best chemical complement, boiling water and the vinegar method are useful adjuncts, and bleach, insecticides, and standalone sprays are the overrated options that leave the breeding site intact.

Which method should I use? A quick comparison

How do I keep drain flies from coming back?

Eradication without prevention just resets the clock. Because drain flies need standing organic film and moisture, prevention is about denying them both. A simple routine keeps drains inhospitable:

• Run water through idle drains weekly. Guest bathrooms, basement floor drains, utility sinks, and rarely used tubs dry out or stagnate; a weekly flush keeps the trap full and the pipe from building a dry crust of gunk.
• Clean drains on a schedule. A monthly scrub with a drain brush, or a periodic enzyme treatment, stops biofilm from reaching breeding thickness.
• Clear hair and food debris promptly. Use hair catchers in showers and tubs, scrape plates before rinsing, and run the garbage disposal with plenty of water.
• Clean the hidden spots. Brush out sink overflow holes, the underside of the disposal splash guard, and strainer baskets, these are the parts people forget.
• Fix moisture problems. Repair slow drains, running toilets, and small pipe leaks that keep organic matter perpetually wet.
• Keep food-waste zones tidy. Empty and rinse recycling and compost bins, and do not let mop buckets or wet rags sit, this also denies fruit flies a home.

Drain fly eradication checklist

Use this as your run-through from first sighting to clean drains:

• Confirmed it is a drain fly, not a fruit fly or fungus gnat (fuzzy, moth-like, resting near drains)
• Ran the tape test on every suspect drain overnight, opening left partly uncovered
• Identified and listed all breeding drains, not just the most obvious one
• Removed stoppers, strainers, and cleared visible hair and sludge
• Poured hot water to soften the film
• Scrubbed each pipe with a stiff brush and drain snake, including overflow holes
• Applied an enzyme or bacterial cleaner and let it dwell overnight
• Repeated treatment nightly for about a week to break the life cycle
• Re-ran the tape test after a week to confirm no new adults are emerging
• Set up a weekly flush and monthly cleaning routine to prevent return
• Called a plumber if flies persisted despite thorough cleaning (possible hidden leak or broken pipe)

How long does it take to get rid of drain flies?

With the breeding drain correctly identified and scrubbed, expect the visible adults to die off within a few days to about two weeks, since they are short-lived and no new ones are hatching once the film is gone. The reason people re-treat for a week is to catch eggs and larvae that were already in the pipe when you started; the drain fly’s egg-to-adult development runs on the order of a week to a few weeks and varies with temperature, so a single night of cleaning rarely gets everything. If you have scrubbed thoroughly, treated every suspect drain, and run the tape test again only to keep catching fresh adults, that is your cue that there is a breeding site you have not reached, perhaps a cracked pipe, a floor drain under an appliance, or a leak keeping gunk wet inside a wall. At that point, a plumber can locate the hidden source.

Key takeaways

Drain flies are a plumbing-film problem wearing the disguise of a flying-insect problem. The adults you see are a symptom; the larvae in the biofilm are the cause. Confirm the breeding drain with the tape test, scrub it mechanically with a stiff brush and snake, follow up with an enzyme or bacterial cleaner over several nights, treat every suspect drain, and then keep the pipes flushed and clean so the film never rebuilds. Do that, and the flies disappear, and stay gone. Skip the scrubbing in favor of a bottle of bleach or a can of spray, and you will be reading this again in a fortnight.