How to Get Rid of Drain Flies in Brisbane Homes: What Works

Drain flies breed in the slime on the inside of the pipe, so how to get rid of drain flies in Brisbane starts with scrubbing that slime off, overflow hole included. Hot water goes down daily after that, and any drain nobody uses gets a plug. Keep it up for three weeks. If flies are still turning up after that, a leak or a cracked pipe is feeding them, and it needs a plumber.

Every adult you swat, spray or trap gets replaced by the next batch growing in the slime on the pipe wall. Killing what’s flying around is mopping the floor while the tap’s still running.

Key takeaways

• Scrubbing the drain body, the overflow hole and the underside of the plug is how to get rid of drain flies, and hot water goes through every day after that.
• Every drain in the house gets a plug when it isn’t in use, including the ones nobody has touched in months.
• Keep treating for at least three weeks, because the breeding cycle runs for two to four.
• Baking soda and vinegar, bleach, fly paper and aerosol sprays leave the larvae in the slime alone.
• Flies that keep turning up after three weeks point to a dirty trap, a leak or a cracked pipe, and finding which one is a plumber’s job.

How to get rid of drain flies, step by step

Removing what the larvae feed on is the whole job, and the first part of it is working out which drain they are coming from.

To find it, lay a piece of clear tape sticky side down across the drain overnight, leaving a small gap so air can still get in. Flies stuck to the tape in the morning mean that drain is breeding them, and a clear cup coated inside with oil does the same job if you’d rather not use tape. Check every drain nearby while you’re at it, because several can be breeding at once.

For anyone working out how to remove drain flies without buying anything, the answer is a stiff drain brush. Work it over the drain body, the overflow hole and the underside of the plug until the grey film is gone. That film is what drain fly larvae feed on, and nothing sold in a supermarket takes it off as well as bristles do.

Showers are the case worth knowing about. The culprit there is often a wad of hair a few centimetres down, past where a brush gets to, and a hair-removal strip from Bunnings pulls it out faster than anything in the cleaning aisle. If the drain was already running slow, how to unblock a drain comes first, so the brush isn’t pushing hair further in.

Very hot tap water goes down daily after that. For buildup, the brush won’t shift; an enzyme cleaner for drain flies digests it slowly and over repeat doses, with Actizyme from Coles as one Australian example.

Look past the drain too. Larvae also develop under leaking pipes, in appliance drip trays, overflow holes, plugs and stoppers, clogged gutters and wet compost, and sink flies often turn out to be coming from the bin or a drip tray rather than the drain.

The cheapest fix nobody does is putting the plug in. Every drain in the house, because plug only the kitchen sink means the drain flies move to the bathroom basin. Overflow holes get covered too: dry them, then tape over them with good-quality clear tape.

Daily for a week, then carry on to at least three weeks. One heroic dose of something nasty fails. Each treatment only catches whichever stage happens to be in the pipe that day, and the rest carry on developing. A brush stops at the opening. If three weeks of scrubbing hasn’t worked, get a plumber in for professional high-pressure drain jetting. It reaches the full length of the pipe.

What are drain flies, and how do you tell them from fruit flies?

They look like tiny, fuzzy moths about 2 to 4 mm long, and you’ll usually find one sitting flat on a bathroom wall near the drain. They don’t fly far. Check that’s what you have before you get into how to get rid of drain flies, because fruit flies and fungus gnats need a different treatment.

They go by several names. Moth flies, sewer flies, and filter flies are the common ones; drain gnats turn up as well, and in the shower they are bathroom flies while in the kitchen they get called sink flies. The scientific family is Psychodidae.

Drain flies vs fruit flies is an easy mix-up to make, and fruit flies are the ones hovering over the fruit bowl: tiny, tan, with red eyes. Fungus gnats are the small black ones circling pot plants. Neither of those comes from a drain, so scrubbing one won’t help. Fruit flies come from the kitchen bin or a potato forgotten at the back of the pantry. For fungus gnats, check the saucers under the pot plants.

Where do drain flies breed, and what are drain fly larvae?

They breed in the film that builds up on the inside of the pipe. It’s gelatinous and made up of soap scum, hair, grease, bacteria and fungi. Drain fly larvae feed on it until they pupate.

A single drain fly lays 15 to 40 eggs in a batch, occasionally up to 100. Anyone who says they have sewer flies or sink flies has drain flies, and the breeding site is the same film. The small black worms in shower drains and basin overflows are the larvae. Slow drains are the first place to look, since a partly blocked drain holds the film in place.

What is the drain fly life cycle?

Two to four weeks from egg to adult, quicker in warm weather, which is why a single treatment never finishes the job. Eggs hatch in as little as 32 hours. Most of the time is spent as drain fly larvae, which feed in the film for 9 to 15 days before a day or two as a pupa. The adult lives about two weeks.

Why do drain flies peak after storms and through a Brisbane summer?

Warm, humid, wet-then-dry weather speeds up drain fly breeding, and spring and summer, especially after storms, are peak season. Brisbane supplies that combination most years.

The damp storms leave behind sticks around. Clogged gutters hold water and overflow holes stay wet. The laundry floor waste is the one nobody remembers: it gets a rush of water and then nothing for weeks, and the first sign is bathroom flies on the wall.

Clear the gutters and run the floor waste before the first big storm. Working out how to get rid of drain flies in February is harder once a colony is established.

Are drain flies harmful?

Drain flies don’t bite or sting and have no interest in your food. What they do point to is organic buildup somewhere it doesn’t belong, and the flies carry bacteria from the drain onto surfaces as they go, so benchtops and basins near an infested drain are worth wiping down. In a heavy infestation, dead flies and fragments can also act as allergens.

Does baking soda and vinegar for drain flies work?

No, it’s mostly theatre. The fizz looks busy, but the two neutralise each other, and nothing reaches the larvae. If you’re going to use one, use one. For a shower or basin, how to remove drain flies comes down to a stiff drain brush, which does more than both combined.

Why does bleach only work for a couple of days?

Bleach is the standard first attempt at how to get rid of drain flies, and for about two days it looks as though it has worked. It does kill what it touches, adults and surface grime included. The drain fly larvae sit protected inside the biofilm, out of its reach, and they are what’s left when the flies return.

Don’t mix bleach with vinegar or any other cleaner, because bleach plus an acid gives off chlorine gas. The same goes for acid drain openers followed by fly spray, or pool chlorine poured down the drain. Stacking product on product puts you at risk and is hard on the pipes.

A septic tank relies on its bacteria, and harsh chemicals kill them. On an acreage block around Logan, Moreton Bay or the Scenic Rim, that is reason enough to stay with a brush and hot water.

Is boiling water for drain flies safe?

Go easy on it. Very hot tap water, or water that has just come off the boil, is the safer habit, particularly with PVC pipes. Toilets are a hard no: boiling water can crack the porcelain.

Does a drain fly trap or drain fly killer help?

A bowl of apple cider vinegar with a drop of detergent shows you how bad the problem is and thins out the adults. That is all it does. Fly paper, UV traps and aerosol sprays are the same: adults only. Insecticide poured down a drain may not work and can damage the system.

If all you want is to know how to remove drain flies already in the air, the vinegar bowl is a fair scoreboard. The larvae are the job.

Why does the bathroom nobody uses breed bathroom flies?

Because the trap seal dries out. Guest ensuites, laundry tubs and floor wastes that rarely see water lose it in about two to three weeks, and what’s left is an open pipe.

The curved P-trap under a basin or sink holds a plug of water, and under AS/NZS 3500 every fixture connects through one. Nothing gets past that water from the sewer side. Flies breeding in the drain body above it were never in the sewer. They hatched in the bathroom. Sewer flies is the wrong name.

Run each tap once a week. Before the Christmas holidays, run every tap in the house before you leave, or ask someone to run them while you are away.

Why do drain flies keep coming back after a thorough clean?

Three weeks of daily cleaning and they are still there: the source is out of a brush’s reach. A dirty trap has to be removed and cleaned. Leaks behind the wall and cracked pipes under the slab are the other possibilities, along with water getting under a failed shower base. Flies coming from where the shower wall meets the floor point to that last one.

A pan-and-tilt CCTV drain inspection shows a crack or leak on screen before anyone digs anything up. If the cause is buildup further along the line, jetting at 4000 PSI and 72 L/min is the job for it. Commercial sites see the same breeding in aircon and refrigeration drain pans.

Repairs to a drain in Queensland are licensed work under the Queensland Plumbing and Drainage Act 2018, so this stage needs a QBCC-licensed plumber. How to remove drain flies fed by a leak is a plumbing question, because the answer is finding and fixing the leak.

Do drain flies mean there is a sewer problem?

Not on their own. Sewer flies is a misnomer, because a healthy trap seal blocks the sewer. They mean organic buildup in or around the drain. The exception is an infestation that returns after thorough cleaning, which points to a crack or leak that needs a camera to confirm.

If three weeks of following this guide on how to get rid of drain flies hasn’t worked, talk to a drainage specialist at SEQ Blocked Drains. We service Brisbane, Logan, Ipswich and the Gold Coast, and we find where they are coming from before we quote anything.