Simple Guide: How to Get Rid of Drain Flies
How to get rid of drain flies by cleaning the gunk they breed in, using a drain brush and enzyme cleaner, and when the problem points to a sewer issue.
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Drain flies are small, fuzzy, moth-like insects that breed in the slimy film lining a drain. Learning how to get rid of drain flies means removing that film and cutting off the damp habitat, while trapping adults helps in the meantime. Expect two to four weeks of cleaning before the flies stop.
Where drain flies come from
Drain flies, also called moth flies, lay eggs on organic buildup inside drains, usually in a sink, shower, tub or floor drain. The film is made of soap, hair, food and bacteria. A drain that is used rarely, such as a guest bathroom or a basement floor drain, is a common source because the water in the trap evaporates and the film dries and stays. Adults are weak flyers and gather near the drain opening.
Quick facts: how to get rid of drain flies
| Quick facts | |
|---|---|
| Time needed | About 20 minutes of cleaning each session, repeated weekly |
| Tools | Stiff drain brush, enzyme drain cleaner, hot water, sticky trap tape |
| Full result | Usually two to four weeks, because each cycle takes time to clear |
| Call a plumber if | Several drains are affected at once, or sewage smell is present |
Step 1: clean the drain itself
Use a stiff brush or an old toothbrush and scrub the walls of the drain opening, the pop-up stopper, and the overflow channel behind the faceplate. The film is usually thickest just below the surface, so work the brush down as far as it reaches. Pull out what comes away and throw it in the trash, not down the drain. This first step is the one that makes the rest of the process work.
Step 2: treat the film with an enzyme cleaner
Pour an enzyme drain cleaner into the drain as the label directs, usually in the evening. This is the step that does the most work in how to get rid of drain flies, because it reaches the film that brushing misses. Enzyme products break down organic matter without harsh chemicals, which makes them a better fit for drain flies than bleach or acid. Leave it overnight, then flush with hot tap water in the morning.
Step 3: trap the adults
Cover the drain opening with a piece of sticky trap tape, or use a small cup of fruit-based bait with a drop of dish soap inside. Adults that land on the tape or sink into the liquid stay trapped. Replace the tape every two to three days and keep the drain covered when you are not cleaning it. Trapping works best alongside cleaning, since it removes adults but leaves the larvae in the film, so keep up both steps for how to get rid of drain flies to succeed.
Step 4: stop the drain drying out
A dry trap lets flies in and gives them a place to breed. Run the tap for thirty seconds every day in a little-used sink, shower or floor drain. This refills the trap with water and keeps the film from drying out between cleanings.
Why drain flies keep coming back
If flies return after two weeks of cleaning, the film is probably deeper in the pipe than the brush reaches. A hidden source can also be a floor drain in a basement, a sump pit or a dishwasher drain line. Check every drain in the home, not just the one where you see flies, because a single source can feed several places. Learning how to get rid of drain flies for good means treating every source the same way: clean the film, keep the trap wet, and trap the adults until the cycle breaks.
Safety when cleaning a drain
Wear gloves and do not mix enzyme cleaners with bleach or other chemical products. If you have used a chemical drain cleaner recently, rinse the drain with water before adding enzymes. Keep children and pets away from the drain while cleaning.
When the problem is a sewer issue
Call a plumber if flies appear in several drains at once, if a sewage smell comes up through the fixtures, or if the flies come back quickly no matter how well you clean. These signs can point to a blocked or broken sewer line, which a plumber can check with a camera.
How to get rid of drain flies: a short plan
To get rid of drain flies, start by identifying which drains are affected, then clean the film inside each one. Repeat the cleaning every few days for two weeks, because the eggs and larvae take time to clear. Adults can be caught with sticky tape placed over the drain opening. If the flies come back after the drain is cleaned, check for a damp floor drain, a leaking pipe or a dry trap that lets flies rise from the sewer. Persistent flies in many drains can point to a sewer line problem that a plumber should inspect.
Keep a note of each step you take, since knowing how to get rid of drain flies depends on repeating the routine consistently. If you learn how to get rid of drain flies in one bathroom, apply the same steps to every drain in the home.
Once the drain is clear, watch for flies for two weeks, since knowing how to get rid of drain flies requires patience.
Related reading
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- Practical Baking Soda and Vinegar Drain Cleaner: Use It Right
- How to prevent a flooded basement: A Step-by-Step Guide
Browse all plumbing guides, or find a plumber in your city from the plumbing directory.
Frequently asked questions
How long does it take to get rid of drain flies?
Most households see a clear improvement within one to two weeks of steady cleaning and trapping. Drain flies complete their life cycle in a few weeks, so a few stragglers can appear for longer even after the source is cleaned.
Are drain flies harmful?
They do not bite or spread disease in a home, but they are a sign of a moist, dirty drain. A large number of them can be a nuisance, and their presence shows that the drain needs cleaning.
Will bleach kill drain flies?
Bleach can kill adults and some larvae on contact, but it does not remove the film that the larvae feed on, so the problem returns. Enzyme cleaners and physical scrubbing work better over time.
Does a drain fly trap work?
Sticky tape and bait cups catch adults effectively, which reduces the number that lay eggs. They do not reach larvae inside the drain, so they must be paired with cleaning.
How to get rid of drain flies if they keep coming back?
Look for a hidden source. Check floor drains, rarely used showers, and the overflow channels of sinks and tubs. If none of these is the cause, a plumber should inspect the drain line.
Can drain flies come from a floor drain?
Yes. Floor drains in basements and laundry rooms are a common breeding site, especially when they dry out. Pour water into them weekly and clean the cover so the film cannot build up.
Do drain flies come from a dirty house?
Not necessarily. They breed in drains and not on clean surfaces, so a spotless kitchen can still have them if a drain is used rarely or stays damp. The source is the drain, not the cleanliness of the rest of the home.
What do drain fly larvae look like?
Larvae are small, grayish and wormlike, and they live in the slime inside the drain. You will rarely see them unless you look into the drain opening, which is why cleaning the film is more useful than searching for them.
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