How to kill sewer gnats

Written by faith mcgee
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How to kill sewer gnats
Remove any food around the kitchen sink when you spray insecticide. (Jupiterimages/Comstock/Getty Images)

Sewer gnats, or drain gnats, emerge from your home's plumbing in the springtime, according to the University of Nebraska. These gnats look very much like fruit flies but do not have red eyes. This particular species of gnat lives off of the bacteria and organic matter that accumulates within the gelatinous lining of your drains and pipes. Severe sewer-gnat infestations indicate that a pipe is broken. By cleaning out your drains and pipes, and removing their main food source, you can kill off sewer gnats.

Skill level:

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Things you need

  • Snake
  • Stiff brush
  • Liquid dish detergent
  • Nonacid, noncaustic bacterial product
  • Pyrethrins
  • Resmethrin

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  1. 1

    Turn on hot water to loosen up the gelatinous material on the sides of your drain and pipes. Remove the drain trap.

  2. 2

    Push a snake into your pipe system by twisting it through the pipes. Scrape the sides of the pipes with the snake while hot water continues to pour down the drain.

  3. 3

    Clean the opening and first 5 inches of drain with a stiff brush. Use 2 tbsp of liquid dish detergent to clean off the sewer gnats' food supply.

  4. 4

    Pour a nonacid, noncaustic bacterial product that eats away at the organic material into your drain. Use the product every day for five days. Incorporate the product into your monthly cleaning routine.

  5. 5

    Spray an insecticide that contain pyrethrins or resmethrin. Insecticides will temporary eliminate sewer gnats until the food supply is gone from the drain and pipes.

Tips and warnings

  • Clean any standing water inside the home that may be under potted plants.
  • Remove trash from the kitchen on a regular basis while getting your sewer gnat problem under control.
  • Avoid pouring bleach down the drain with ammonia-based cleaning products; the chemicals create a toxic reaction when used together.

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