How to Get Rid of Drain Flies (for Good!)

Drain flies, also called sewer flies, sink flies, or filter flies, are common household pests that live and feed on organic matter found in any place with shallow, stagnant, or standing water. They do not bite, sting, or transmit diseases, so they are generally not harmful to humans or pets. But they can be quite a nuisance, especially when they show up in large numbers.

Large drain-fly infestations, however, can cause health risks. Since they tend to hop around, they can quickly transfer bacteria and contaminate surfaces, including any food left out on countertops. They can also worsen bronchial asthma symptoms. When left en masse for long periods in a vacant home, they can plug pipes and cause costly damage. So how do you get rid of drain flies for good?

What Are Drain Flies?

 "Drain flies are small flies that are often found in and around drains, sinks, and other areas with standing water," says Matthew Kunz, president of Mr. Rotter Plumbing. They can enter homes through open windows and doors, and "are attracted to the organic matter present in these locations. Drain flies lay their eggs in moist, organic materials like the sludge and buildup found in drains, sewage systems, or stagnant water. The eggs hatch into larvae, which feed on the organic matter and develop into pupae and, eventually, adult flies."

Drain flies have small, round, fuzzy bodies measuring about 1.5 mm to 5 mm long. They have six legs and can easily be identified by their moth-like wings with unique veins or erratic flying patterns. Drain flies are poor fliers. Instead, they tend to hop from surface to surface or fly for short distances.

That’s one way you can tell them apart from other kinds of flies, says Kari Warberg Block, founder and CEO of EarthKind. Other flies have stronger wings and can fly longer distances. She says that with drain flies, you will rarely see the eggs, larvae, or pupa, “but you will see adults. The adult drain fly is grayish brown, approximately 4 mm long, and looks hairy due to the scales on the wings.”

Where Do Drain Flies Come From?

To get rid of drain flies, you first have to know where they're coming from. Drain flies tend to hang near their breeding ground, so once you spot them, check the nearby drains. Sometimes, the breeding ground can be outside your house, including compost piles, animal waste, storm drains, garbage collection sites, birdbaths, or barns.

To check your pipes for drain flies, use the following methods.

Duct Tape Test

“By placing tape over the suspect drain for 24 hours, you can confirm if you found the problematic drain line,” says Warberg Block. If you find flies stuck in the tape, you have found the breeding source. “Once you know where they are coming from, you can focus on removing the fly's food source,” she adds.

Check for Larvae

Checking for adult drain flies is recommended over finding larvae. After all, drain fly larvae are incredibly small and, usually, they are deep within the pipes. But if multiple duct-tape tests fail, you can open your drain cover, remove any gunk, and search for long tube-like larvae. If you find them, “start by cleaning your drains and pipes thoroughly. Use a pipe brush or drain snake to remove any organic material, hair, or sludge that might be providing a breeding ground for the flies," says Kunz.

How to Get Rid of Drain Flies

To eliminate drain flies, you have to prevent them from accumulating in the first place. Kunz says to focus on any sources of standing water in and around your home, such as clogged gutters, leaky pipes, or waterlogged potted plants. Keep kitchen and bathroom areas clean. Clean up spills, crumbs, and food residue promptly. Also, regular plumbing maintenance can prevent future buildups of organic matter.

Natural remedies for cleaning drains include:

Vinegar and baking soda: Pour down the drain 1/2 cup baking soda and 1 cup of vinegar. Plug the drain and allow this mixture to sit for a while—it eliminates clogs. Then, rinse the drain with hot boiling water.

Boiling water: “The most natural way to remove the biofilm is to flush the drain with boiling water and then clean the drain with a metal pipe brush,” says Warberg Block.

Homemade drain fly traps: Place a solution of apple cider vinegar and dish soap in a shallow dish. "The flies will be attracted to the vinegar and get trapped in the soap," Kunz advises.

Microbial drain cleaner: An enzyme or microbial-based drain cleaner will feed on the biofilm and remove the food source and larvae.

Seek a professional’s help before trying any chemical methods. Standard non-natural options include using peracetic acid (4000 ppm) or bleach to eliminate buildup in the drain pipes. However, bleach may permanently damage your septic tank and, since bleach flows quickly, it may not be fully effective in removing thick buildup, eggs, and larvae. Traditional store-bought drain cleaners, chemical sprays, and repellents also help eliminate adult flies. Last, insect growth regulators, like Gentrol Aerosol, can prevent adult drain flies from laying eggs.