The longer and more flexible your pipe brush, the better! If you’re treating the drain of a sink, remove the U-trap underneath and clean out any additional buildup you find.

This method is more effective for killing larvae inside the pipes than adults that can fly. PVC pipes can be damaged by repeated or prolonged exposure to boiling water, so it’s recommended to only use this method for metal pipes. If you have PVC pipes, stick to pipe brush cleanings and cleaners meant for kitchen and bathroom drains.

Start by using ½ cup (64g) each of salt and baking soda and 1 cup (250 ml) of vinegar. For deep pipes or severe infestations, increase the amounts proportionately. Try sprinkling the baking soda and salt in and around the dain first and then pouring the vinegar so the mixture doesn’t foam before it enters the drain. PVC pipes can be damaged by boiling water. Flush the vinegar mixture away with warm water from the tap if you have PVC pipes.

Add a chunk of overripe fruit to the vinegar to make the bait extra appealing. A few drops of dish soap makes it harder for the flies to escape the vinegar. Another trap can be made by mixing water, sugar, apple cider vinegar, and a few drops of dish soap in a bowl. Sit the bowl (uncovered) near the infested drain for a few days to lure the flies into the deadly solution.

This method is effective if you only need to kill a few drain flies now and then.

Enzyme cleaners are non-toxic and made for kitchen use. Once the drain is cleared of buildup and larvae, the flies will begin to disappear.

Some natural and environmentally friendly cleaners can be found online or in most hardware or home goods stores. Read the labels carefully to find a product that targets organic matter.

An insect growth regulator (IGR) spray can prevent drain fly eggs from hatching and keep larvae from maturing into adult flies. Chemical sprays and repellents should be considered when traditional cleaners or enzyme gels are insufficient to kill or prevent drain flies. There are no insecticides approved for drains or sewage systems, and pouring them down the drain can severely damage your pipes or septic system. [9] X Research source

PVC pipes can be damaged by boiling water. If you don’t have metal pipes, stick to a cleaner meant for kitchen or bathroom drains instead. If there’s a drain that doesn’t get used often, make a point to run water through it at least once per week. If you’re going to be gone for days or weeks and are worried about drain flies, close your drains with a stopper so no bugs can move in while you’re away.

If there are multiple drains nearby, duct tape the drains shut overnight and inspect the sticky side the following morning to see which one the flies are coming out of. While you treat your drain, adult flies can be killed with vinegar traps, fly swatters, or indoor-safe bug repellents.

From egg to adult, a drain fly lives 21 to 27 days. You probably won’t see them until they are adults (the last 7 or so days of their life).

Drains that are rarely used or poorly maintained are more prone to drain fly infestations than regularly used drains. Since adult drain flies cannot fly very far, they will usually gather near their home drain. This makes it pretty easy to identify the source of the infestation. Compost, animal waste, and garbage are appealing food sources for drain flies.

The fine, hair-like scales on drain flies can fall off and be inhaled. This might cause irritation for those with sensitive respiratory systems.

Check a drain for flies by taping the drain shut overnight and examining the sticky side the following morning for trapped bugs. Check for larvae by removing your drain cap and scraping the inside of your pipes. Look for thin, tube-like larvae in the sludge. If you don’t see larvae but are certain you have a drain fly problem, it’s possible that the eggs are being laid deeper in your pipes.