The good news is most drain fly issues can be fixed within about a week with regular cleaning and careful attention.
The simplest method to clear out your drain fly issue is to pour boiling water carefully down your drain 1-2 times a day for about a week. This will ensure that the flies do not return overnight if the water did not catch all of the organic material built up inside.
Adult flies emerge from the breeding sites but may remain nearby. Drain fly control often fails because people don't realize just how resistant the scum and the larvae are to boiling water, bleach, detergent, and even caustic drain cleaners (see How Can I Get Rid of Drain Flies?).
What Causes Drain Flies? Drain flies thrive in stagnant and standing water. Common sources include slow or clogged drains, rarely used and unused toilets, refrigerator drain pans, and standing water created by leaking pipes. They typically enter buildings through basements, windows, and drains.
During the day, adults rest in shaded areas or on walls near plumbing fixtures and on the sides of showers and tubs. Most activity occurs during the evening when these flies are seen hovering about drains and sinks.
Mix together 1/2 cup of salt, 1/2 cup baking soda and 1 cup of vinegar. Pour the mixture down the drain. Let sit overnight, then flush the drain with hot water in the morning. This should kill all flies and the organic material they've been feeding on.
Behavior: Drain flies are most active at night. They are weak flyers that make short hopping flights of a few feet when they are disturbed. Drain flies rest on surfaces with their wings held over their back like a roof. You'll usually find a drain fly close to its breeding ground.
Do Drain Flies Die in Winter. Most fly species cannot survive outside temperatures below 32°F (0°C). They die unless they find a warm and conducive place to overwinter, such as your home. Drain flies are one of the few insects that can tolerate cold weather conditions.
Lavender, eucalyptus, peppermint, lemongrass, and citronella are just a few of the scents that insects despise (with lavender probably being the most effective). Pouring half or an entire cup of such essential oil onto a sponge or rag, then storing it in a small can, helps keep flies at bay.
These pests are a nuisance because they infest in large numbers. Once inside, drain flies may plug pipes and spread bacteria from the filth they live in, possibly contaminating food in the process. These pests, even though they live in filth, are not known to spread any disease to humans.
One common remedy for killing drain flies is using household bleach. This is a very useful and cost-effective manner for getting rid of these little pests with an item you already have around the house.
Baking Soda, Boiling Water & Vinegar
The pour half a cup of bicarb soda down the sink as well, followed by a half cup of white vinegar. Let it settle for a few minutes then poor some more boiling water down the drain. Follows these steps every few days until the drain flies have completely disappeared.
For effective drain fly treatment, use three products: Forid Drain Gel Cleaner, Gentrol IGR Aerosol, and Pyrid. Forid is an organic microbial grease degrader that breaks down organic material and waste, which will eliminate their food sources and their breeding grounds.
They do not bite, sting, or spread diseases, but their decaying bodies may cause allergic reactions. They can also spread bacteria from trash, decaying vegetables and fruits. Drain flies breed in areas that are moist and have a lot of organic remains, including: Sinks.
Drain flies are typically only found in the summertime or in places with moderate year-round climates. Cold weather kills off more drain flies than any of their predators. If drain flies are able to find a home indoors, they can continue their development throughout the year, even during the winter.
"Combine 1/2 cup salt with 1/2 cup baking soda and 1 cup of vinegar and pour down the drain." Leave it overnight, and in the morning, pour boiling water down the drain. "This is a natural remedy that will clean the plumbing pipes and remove the breeding grounds for these flies," he explains.
To make an all-natural drain fly trap, fill a bowl with apple cider vinegar and cover it with plastic wrap. Punch small holes in the wrapping. The vinegar's smell will attract the drain flies, and the wrap will trap them inside the bowl. Another option is to mix a few drops of dish soap with a cup of vinegar.
Sources of Drain Flies
They can live most anywhere that water accumulates for a week or more. Common indoor sites include the fine slime layer that develops along the water surface in infrequently used toilet bowls and tanks, in sink or floor drains in basements or garages, or drain pans under refrigerators.
Drain flies, also known as sewer flies, filter flies, moth flies or sink flies, look similar to the average house fly as they are very small – about an eighth of an inch – and black/brown. They also have a unique vein pattern in their wings, which are covered in tiny hairs. They leave a powdery smudge when crushed.
Most exterminators use chemical methods and habitat modification to kill all eggs, larvae, and adult drain flies (removing food sources, etc.).
Some species hold the wings out to the side, which gives them a moth-like appearance—hence the name "moth fly." They are weak fliers and make irregular, hesitating flights covering only a few feet in short, jerky lines. Eggs are tiny, brown or cream-colored and are laid in irregular masses of 10 to 200.
Preventative Maintenance
Pouring bleach into the drain when the unit is not operating can leave residual bleach, which will damage the drain pan and line. Using vinegar for preventative maintenance throughout the year will keep your drain clean and clear and will not damage your line.
Drain flies gather, mate, and lay eggs in moisture or standing water. The slimy film that forms in sewers and drains is a favorite breeding spot. Inside structures, they are strongly attracted to light and will be found on glass windows, doors, lamps, and indoor lighting.