To get rid of drain flies, find the drain they are breeding in, scrub out the slimy film inside it, then keep that drain clean and in regular use. Sprays only kill the adults you can see, while the larvae keep developing in the build-up below.
Below, you’ll learn how to get rid of drain flies for good: confirm what they are, find the exact drain with an overnight tape test and clear it without harming your pipes. We also cover bathroom floor wastes, outdoor gully traps, apartments with shared pipes and the signs that point to a plumbing fault.
Last reviewed: 3 November 2026
What Are Drain Flies?
Drain flies are small, grey, fuzzy insects with wings that look like a tiny moth’s. You may also hear them called moth flies, sewer flies or filter flies.
They fly weakly, in short hops, so you usually see them resting on a wall, mirror or shower screen near a drain. The Australian Faunal Directory records one moth fly species, Clogmia albipunctata, in NSW and notes that its larvae live in wet domestic habitats.
Drain Flies or Fruit Flies?
It’s worth being sure before you start cleaning, because the two pests need different fixes.
| Clue | Drain flies | Fruit flies |
|---|---|---|
| Look | Fuzzy, grey, moth-like wings | Smooth tan body, often red eyes |
| Flight | Short, fluttery hops | Quick, hovering |
| Where you see them | Walls and screens near drains | Fruit bowls, bins and bottles |
| Where they breed | Slimy film inside drains and traps | Ripe or fermenting food |
Flies gathering around a fruit bowl or bin are fruit flies, and cleaning the drain won’t help. Flies resting near a sink, shower or floor waste are most likely drain flies, so read on.
Drain Fly Larvae and Their Life Cycle
Drain fly larvae are small, legless, greyish worms just under a centimetre long, with darker tips at each end. They live in the slimy, bacterial film that coats the inside of drains and overflow pipes.
Entomologists at Ohio State University put the full life cycle at one to three weeks, and they note the larvae are surprisingly resistant to bleach. That explains why pouring products down the drain so often fails while the film stays in place.
Adults are the stage you notice, but they are only part of the problem. Kill them without removing the film and fresh adults keep emerging, which makes it look as if the treatment failed.
The Tape Test: Find the Breeding Drain
Before treating anything, work out which drain is responsible. Guessing usually means cleaning the wrong one.
- List the drains you suspect: basins, showers, the kitchen sink, the laundry tub, floor wastes and any drain in a room you rarely use.
- Dry the rim around each opening.
- Lay a strip of clear tape, sticky side down, across each opening, leaving a small gap at one edge for air.
- Leave the tape in place overnight.
- Check the underside of each strip in the morning.
Flies stuck to the tape show you the breeding drain. It is often one you wouldn’t have picked, such as a guest bathroom basin or a laundry floor waste.
If no tape catches anything after two or three nights, the source may not be an indoor drain at all. The sections on outdoor gullies and hidden sources below cover where else to look.
What Causes a Drain Fly Problem?
Build-up inside the pipe
Soap residue, hair, grease, skin cells and food scraps form a soft film on the pipe wall. That film is where drain flies lay their eggs and what their larvae feed on.
Drains that rarely get used
A spare bathroom, an unused floor waste or a basin in a granny flat can go weeks without fresh water. Nothing disturbs the film, and the water in the trap slowly evaporates.
Leaks and standing water
A slow drip under a vanity, a cracked trap or water sitting under a floor can keep a colony going. In that case the flies may have little to do with the drain itself.
A slow or partly blocked drain
A drain that runs slowly as well as producing flies is usually holding wet waste in the line. Our guide on how to unblock a sink drain covers clearing it before you treat for flies.
How to Get Rid of Drain Flies Step by Step
Knowing how to eliminate drain flies comes down to removing the film they breed in, so work through these steps in order on the drain the tape test identified. The first two steps do most of the work, and the rest support them.
Step 1: Lift the grate and clean what you can see
Remove the plug, strainer or floor waste grate and scrub off the grey slime on and under it. Wear rubber gloves and wash the grate in hot, soapy water before you put it back.
Step 2: Scrub inside the pipe
Push a long, flexible drain brush down the opening and work it up and down the pipe wall. This strips away the film the larvae live in, which nothing you pour in can match.
Researchers at the University of Kentucky name thorough cleaning of pipes and traps as the most effective control. A brush made for drains reaches much further than a bottle brush.
Step 3: Rinse with hot tap water
Run hot water from the tap for a minute or two to carry away what the brush loosened. Hot water alone only gives short-term control, so treat it as a rinse rather than a cure.
We don’t suggest pouring kettle after kettle of boiling water down the drain. Most drain pipes in Australian homes are PVC, which pipe makers rate for continuous flow up to about 60°C, so keep boiling water away from basins, toilets and plastic waste pipes.
Step 4: Follow up with bicarb soda and vinegar
Half a cup of bicarb soda followed by half a cup of white vinegar can loosen light residue and freshen the drain. Let it fizz for about 15 minutes, then rinse with hot tap water.
It helps after scrubbing but won’t shift a thick film on its own. Our guide to bicarb soda and vinegar for drain cleaning explains what the method can and can’t do.
Step 5: Try an enzyme drain cleaner
Enzyme or bacterial drain cleaners digest organic film slowly and are generally gentler on pipes than caustic products. They suit follow-up and regular maintenance more than the first clean-out.
Step 6: Set a vinegar trap for the adults
A small bowl of apple cider vinegar with a drop of dishwashing liquid, covered in cling wrap pierced with a few holes, will catch adults still flying around. It does nothing to the larvae in the drain, so use it alongside the cleaning and never instead of it.
Step 7: Repeat after a week
A second scrub catches anything you missed and removes film laid down since the first clean. Expect a few stragglers for a week or two while flies already in the pipe finish developing.
Commercial cleaners and insect sprays
Strong caustic or acid drain cleaners are rarely needed for drain flies, and the larvae cope with harsh products better than you might expect. If you do use one, follow the label exactly, wear gloves and eye protection, and keep the room well ventilated.
The NSW Poisons Information Centre advises against mixing chemicals, so never combine drain cleaner, bleach or vinegar, or pour one straight after another. Tell your plumber what you’ve used before they open the drain.
Insect spray won’t solve it either. It kills the adults you can see and leaves the larvae in the pipe untouched.
Drain Fly Treatments Compared
Some remedies do far more than others. This table shows what each one actually achieves.
| Method | What it does |
|---|---|
| Drain brush | Removes the breeding film The most effective single step |
| Hot tap water | Rinses away loosened material Short-term only; skip repeated boiling water |
| Bicarb soda and vinegar | Loosens light residue and freshens Helpful, not enough on its own |
| Enzyme cleaner | Digests film over time Good for follow-up and maintenance |
| Vinegar trap | Catches flying adults Leaves the breeding source untouched |
| Insect spray | Kills adults only New flies soon follow |
| Bleach or caustic cleaner | Rarely clears the film Burn risk; never mix products |
Source: University of Kentucky and Ohio State University entomology fact sheets, NSW Poisons Information Centre.
Bathroom Drain Flies: Showers and Floor Wastes
When you see drain flies in bathroom drains, they usually come from the shower waste or the floor waste rather than the basin. These drains collect hair, soap and skin, stay damp and rarely get cleaned below the grate.
Lift the grate, pull out any hair and scrub the visible pipe below it with a drain brush. Clean the underside of the grate too, since slime often builds up there unseen.
A floor waste in a laundry or second bathroom may only get water when the floor is mopped. Pour a bucket of water into it every week or two so the trap stays full and the film never settles.
A toilet that is rarely flushed can hold slime under the rim and in the bowl as well. Flush it and give the bowl a scrub each week.
Outdoor Gully Traps and Other Outside Sources
Most Sydney houses have an outdoor gully: a grated drain near the laundry or kitchen wall where the wastewater pipes meet. In NSW this is often an overflow relief gully, and Building Commission NSW rules set its grate below the lowest fixture inside and above the surrounding ground so a sewer blockage overflows outside first.
Gullies dry out in hot weather and collect leaves, soil and food waste around the grate, which can keep sending flies indoors however well you clean inside. Clear debris off the grate, rinse the gully with a bucket of water and keep garden beds and mulch below the grate.
Never cover or seal the grate, and leave anything beyond lifting and rinsing it to a licensed plumber. A cracked, sunken or buried gully is a drainage repair, not a cleaning job.
Drain flies can also breed outside the plumbing. University of Kentucky entomologists list low, wet areas where air conditioners drain and clogged gutters among their preferred breeding spots.
Apartments With Shared Waste Pipes
In a unit, the breeding site may sit in a pipe you share with the apartments around you. Flies that appear in several units, or that return after you’ve cleaned every drain you can reach, point to a shared line.
The NSW Government lists pipes among common property, and the owners corporation is responsible for repairing common property. Owners should raise it with their strata manager or committee, and tenants with their landlord or agent.
The pipes and trap under your own sink, basin and laundry tub are usually yours to look after. Keep those clean while the shared line is checked.
Why Drain Flies Keep Coming Back
If flies return after two thorough cleans, the source is usually somewhere you can’t reach. A plumber will usually look for one of three causes.
- A hidden leak under a slab, inside a wall cavity or beneath a vanity that keeps the area damp.
- A cracked or sagging pipe that holds waste and water in a low spot.
- A partly blocked line further down, where wet waste sits beyond the reach of a brush.
A water meter that moves while every tap is off is a common sign of a hidden leak. Our guide on finding a leak when the water meter keeps spinning walks through that check.
Finding and fixing these faults is a job for a professional, because NSW licensing rules require a licence for any plumbing or drainage work, whatever its size. Opening walls, cutting into drains or lifting fixtures off their pipes is not DIY.
A camera inspection shows what is inside the line, including cracks, sags and build-up a brush can’t touch. Our drain camera inspection service pinpoints where the problem sits before any digging is considered.
How to Keep Drain Flies Away
Once the flies are gone, a little routine stops the film from building up again. These habits take minutes rather than hours.
- Brush and rinse problem drains every few weeks.
- Run water through unused drains, floor wastes and toilets every week or two.
- Fit strainers in sinks and showers to catch hair and food scraps.
- Fix drips and leaks promptly, inside and outside.
- Keep the outdoor gully grate clear of leaves and soil.
Why drain flies are worse in summer
Drain fly development slows in cool weather and speeds up as temperatures rise. A drain that produced the odd fly in July can be much busier by January, so step up the routine over a Sydney summer.
Seldom-used drains also dry out faster in the heat, which leaves the film undisturbed for longer. If a drain smells as well as breeding flies, our guide to getting rid of drain smells covers that side of the problem.
Frequently Asked Questions
How do I permanently get rid of drain flies?
Remove what they breed in: find the drain with a tape test, scrub the film off the pipe wall and keep that drain in regular use. Treatments that only kill adults won’t last.
Does pouring vinegar down the drain kill drain flies?
Not reliably on its own. Vinegar can loosen light residue, but the larvae live in a film that scrubbing removes far better, and a vinegar trap only catches adults.
Will bleach or a chemical drain cleaner kill drain flies?
Rarely on its own, because the larvae are surprisingly resistant to bleach and the film protects them. Drain cleaners can also cause chemical burns, according to healthdirect, so read the label, wear gloves and never mix products.
Are drain flies harmful?
They don’t bite and are mostly a nuisance. Ohio State University entomologists note they may carry microbes from drain slime onto surfaces, so it makes sense to clear them rather than live with them.
Why do I have drain flies when my drains look clean?
Check floor wastes, rarely used toilets, the outdoor gully, air conditioner drip areas and any hidden leak. In apartments, a shared pipe can produce flies in several units at once.
How long does it take to get rid of drain flies?
Numbers usually drop within a few days of scrubbing the right drain, with stragglers for a week or two. If nothing changes after two weeks, the real source probably hasn’t been found.
When to Call a Plumber About Drain Flies
Most drain fly problems end with a brush and some patience, but some point to the plumbing itself. This table shows where the line sits.
| What you see | Who should handle it |
|---|---|
| Flies from one basin, shower or floor waste | Safe to clean yourself Lift the grate, scrub and rinse |
| Flies return after two thorough cleans | Licensed plumber Camera inspection to find the hidden source |
| Drain is slow, gurgling or smelly too | Licensed plumber Likely a partial blockage further down |
| Damp floor, wall or vanity cupboard | Licensed plumber Possible hidden leak |
| Outdoor gully cracked, sunken or buried | Licensed plumber Drainage repair |
| Flies in several units of one building | Strata manager or landlord Shared pipes are common property |
Source: NSW Government plumbing licence and strata repair guidance.
Rapid Service Plumbing works across Sydney, and our blocked drain service covers inspection and clearing when a drain fly problem turns out to be a plumbing one. If you’ve scrubbed every drain twice and the flies keep coming back, it may be time to have someone take a look.
This guide is general information. Plumbing, drainage and gas work in NSW must be done by a licensed tradesperson.
