Will bleach kill drain flies? Mostly, yes, bleach kills drain flies fast but also comes with downsides. The pesky, little black flies you saw could be drain flies. These tiny flies, also commonly known as sewer flies, are usually not harmful but can be a sign of a much bigger issue with standing water and a clogged drain.

Will bleach kill drain flies


What does drain fly look like?

Drain flies are tiny flies that frequent your shower drains, sinks in the kitchen, and bathroom. These critters are similar to larger house flies in features—they have six legs, two wings, and antennae.

Contrary to popular belief, most people think they are black, whereas they are actually grey in color with little hair covering their body, giving them a rather fuzzy appearance.

A lot of these characteristics are so little that you would require a microscope, and not bare eyes, to see them. Drain flies can grow to a maximum adult length of 4-10 millimeters.


Drain flies usually cluster and mate in areas with standing water. They eat organic debris that builds up or gets stuck in your pipeline, which can be anything from hair in a shower drain to vegetable peels in your kitchen garbage disposal. They typically lay their eggs in the congested region, and the eggs develop into larvae living at your disposal.

Drain flies have a very short life span. Entomology research at Cornell explains that drain flies may go through the life cycle in 1-3 weeks. The adults can live up to 2 weeks after emerging. The eggs are typically laid in irregular masses in places like water traps in plumbing fixtures, garbage disposals, built-in sinks, or any moist place with decaying organic matter. Drain flies are holometabolous insects that go through egg, larval, pupal, and adult life stages (as published on the University of Florida website). When they become adults, they go in search of food.

Will bleach kill drain flies?

Using home bleach is a common home remedy for killing drain flies. This is a highly practical and economical method with your bleach already handy in the house.


Most drain flies will be eliminated with just a cup of household bleach. All you need to do is pour it down the infected drain or area. It might take a few hours or a day to completely kill the adult flies with bleach. Moreover, the chemical is potent enough to kill the larvae.

To prevent skin burns in the case of spillage, handle bleach with extreme caution and wear protective gloves.

If you have a septic system, using bleach on drain flies is not advisable. Your septic tank bacteria condition might be quite delicate. The microbes in your tank could be killed with excessive bleach, so you want a milder solution.

You can mix ½ cup of salt with ½ cup of baking soda, and 1 cup of white vinegar as a safer substitute for bleach to kill drain flies in your home.

The following morning, pour hot water over the mixture after allowing it to sit overnight in the drain.

Compared to using bleach, this method is safer for your plumbing. It is only preferable to apply bleach as a final resort after exhausting all other options.

Below are reasons you don’t want to get rid of drain flies using bleach solution (especially if undiluted):

  • When bleach is mixed with other chemicals such as ammonia, vinegar, or rubbing alcohol, it tends to produce toxic hazardous vapors. If you inhale the resulting fumes, you will experience breathing difficulties, respiratory harm, and chest pain, and it can be lethal in extreme cases. Thus, only mix bleach with water if you decide to use it to eliminate drain flies.
  • Undiluted bleach poured down domestic drains can harm your septic system permanently. Peter Urban on AARP explains that “higher concentrations are potentially harmful overkill”.
  • If bleach is mixed with inappropriate chemicals, inside your pipes, it can potentially harm the plumbing in your home. Lead or plastic pipes may eventually corrode as a result. Older pipes are particularly vulnerable to corrosion and bleach damage.

How much bleach to kill drain flies

The depth of infestation determines how much bleach you need to kill drain flies. In general, the recipe calls for a bleach water ratio of 1 to 10.

  1. Mix 1 part bleach to 10 parts water.
  2. Apply your solution to the drain.
  3. Allow up to 4 hours.
  4. Pour cold water into the drain.

Bleach might be effective, but it lacks the scouring power in baking soda and salt for when cleaning pipes and removing the larvae.

That said, how long does it take for bleach to kill drain flies? Bleach is strong enough to kill the larvae and adult drain flies within a few hours or a day.

Are drain flies resistant to bleach?

It isn’t uncommon for drain flies to be resistant to bleach due to their short life cycle and ability to quickly reproduce. When you bleach a drain, it may kill some of the drain flies, but it is unlikely to completely eliminate an infestation. Additionally, bleach can be harmful to your pipes and septic systems if you use it in large quantities. Thus, it is generally not recommended as a method of control for drain flies.

Other methods may be more effective at eliminating drain fly infestations, such as physically removing the breeding sources, using a biological control agent like Bacillus thuringiensis, or applying a chemical insecticide.

It is always a good idea to follow the instructions on any pest control product and take necessary precautions to protect yourself and your home.

If you choose bleach as a drain fly control method, consider the following steps:

  • Search for the infestation root. You may want to inspect the drains in your kitchen, bathroom and basement drains, because drain flies are usually found next to drains.
  • Clean your drains at all times. Use a mixture of bleach and water to clean the drain or use a drain cleaner. Endeavor to remove every possible organic material that the flies may likely feed on.
  • Apply a bleach solution. In a spray bottle, sprinkle bleach and water in equal parts. Spray the remedy into a drain as well as any nearby surfaces where you have observed drain flies.

Repeat this process regularly to keep the drain flies at bay.

When handling bleach, avoid getting it on your skin or in your eyes, and use gloves. Bleach can release toxic gasses, so make sure the area is properly ventilated before application

Get rid of drain flies naturally

If you decide bleach is not worth it in your situation, consider the following natural remedies:

1. Baking soda

  1. Pour ½ cup each of baking soda and salt followed by 1 cup of white vinegar in the drain.
  2. Allow to sit overnight. 
  3. By morning, pour a pot of boiling water into the drain.
  4. Repeat this process weekly or twice a week until you stop seeing drain flies.

2. Vinegar

Leave a bowl of vinegar, soap, sugar, and water on the kitchen counter to attract and drown the drain flies in the soap.

If apple cider vinegar is all you have, that might also be effective. It should be poured into a container and completely wrapped with plastic. Make a few tiny holes in the plastic so that the drain flies can enter but not exit the container.

3. Hot water

Pour hot water into the drain about once or twice a week until you no longer notice the drain flies.

Preventing drain flies from returning

When washing your dishes, if you see these fuzzy flies coming out of your drain, then it is time to clean up your home. Note that drain flies may sometimes not come from the drain only.

1. Spot the breeding area

To detect the fly’s breeding site, perform a thorough search on places including:

  • drains
  • filthy trash cans
  • saucers under potted plants
  • birdbaths or feeders
  • clogged roof gutters
  • clogged storm drains
  • air conditioners
  • cooling towers
  • moist compost
  • rain barrels
  • septic tank
  • sewer

Except for the adult drain flies, the issue is resolved once the organic matter, alongside the larvae, is removed.

2. Clean your drains

Using your typical drain cleaner won’t solve the issue. Pest exterminators apply foaming enzymes that break down the film coating drain flies feed on, and may as well target the drain fly eggs to prevent future infestation. This is a safe treatment that won’t also harm plumbing.

Using an ultra-low volume (ULV) fogging machine is another method for eliminating drain flies. However, this method does not permanently handle the breeding site problem, so it’s not a long-term solution.

3. Seek professional assistance

It may be time to bring in experts for assistance with any slow, partial, or serious drain clog problem you may be facing while trying to get rid of drain flies.

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