Drain flies, also known as sink flies, sewer gnats, or filter flies, are a tiny, common household pest that thrive in moist environments like drains, sewers, and septic tanks. They look like fruit flies, and their presence can be a similar annoyance, but they will only appear near stagnant water. This is important to know because a drain fly infestation can indicate issues like clogged pipes or leaks. If you’ve noticed these pests buzzing around your sinks or drains, it’s important to tackle the problem at the source.

You'll Need

  • Pipe brush or drain scrubber
  • Boiling water
  • Baking soda
  • White vinegar
  • Bleach (optional)
  • Drain cleaner (enzymatic cleaner preferred)
  • Fly traps (sticky traps or homemade solutions)
  • Rubber gloves

1. Identify the Source

  • Locate the Drain: Drain flies typically breed in moist environments with organic matter. Check your sinks, bathtub drain, and basement floor drain.
  • Test for Activity: Cover suspected drains with clear plastic wrap overnight. If flies are trapped on the plastic by morning, you’ve found the source.
  • Inspect Nearby Areas: Ensure that garbage disposals, overflows, and other damp areas aren’t also harboring flies.
Dirty sump pump in a basement.
Is your sump pump breeding drain flies? Credit: Emily Fazio

2. Clean the Drain

  • Scrub the Drain: Remove the drain cover and use a drain brush or pipe cleaner to scrub inside the drain, removing any organic matter or sludge where flies may breed.
  • Pour Boiling Water: Carefully pour boiling water down the drain to eliminate eggs and larvae clinging to the pipe walls. Repeat several times for the best results.
  • Apply Baking Soda & Vinegar: Pour 1 cup of baking soda into the drain, followed by 1 cup of vinegar. The mixture will fizz, helping to break down any organic buildup. Leave it for at least 30 minutes, then flush with more warm water.

3. Use a Drain Cleaner

  • Apply Enzymatic Cleaner: For more persistent infestations, use an enzymatic drain cleaner that breaks down organic material inside the pipes. Follow the product instructions for the best outcome.
  • Repeat Regularly: Continue applying the cleaner as per the recommended schedule to prevent future infestations. Enzymatic cleaners are eco-friendly and safe for most drains.

4. Set Traps for Adult Flies

  • Use Sticky Traps: Set up sticky fly traps near the affected drains to capture adult flies. These traps help reduce the fly population while you treat the source.
  • Homemade Vinegar Trap: Create a trap by filling a small container with apple cider vinegar and a drop of dish soap. Place it near the drain to attract and trap the flies.
Small insects trapped on a ZEVO Blue Light UV Trap.
A blue light/UV trap can help lure and trap drain flies. Credit: Emily Fazio

5. Prevent Future Infestation Problems

  • Maintain Clean Drains: Simply keeping drains clean is the easiest prevention method. Scrub them and using the boiling water method to keep them free of debris and buildup.
  • Fix Leaks and Damp Areas: Repair any leaking pipes, clogged drains, or areas with standing water to avoid future breeding grounds.
  • Use Enzyme Cleaners Monthly: As a preventive measure, apply an enzymatic cleaner monthly. The chemical reaction will clear your pipes and take care of any drain fly larvae.

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FAQ

What attracted these drain flies?

Drain flies are attracted to standing water and a food source. They can occur in kitchen sinks, bathroom drains, storm drains. Anywhere with moisture and a buildup of sludge, food residue, or soap scum provides an ideal environment for them to breed and lay their eggs. The ideal moist environment can also appear if there’s a plumbing issue like a slow drain or leak.

Are they harmful?

While drain flies are annoying, they don’t bite or spread diseases. However, an infestation of drain flies can be an indicator of unsanitary conditions or leaky pipes. A large infestation may also worsen allergies or asthma due to the accumulation of fly carcasses and debris.

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How long will it take to get rid of drain flies?

If you address the infestation promptly with a thorough drain cleaning or fixing leaky pipes, it can take 1-2 weeks for these bothersome pests to die out. Persistence is key, and applying enzyme drain cleaner, a chemical spray, or flushing the pipes with warm water should be done diligently. The key is to clean the pipes to keep the eggs from hatching. Setting out apple cider vinegar traps can help catch any lingering adult drain flies too.