How to Get Rid of Drain Flies in Commercial and Industrial Buildings

Are drain flies taking over your sinks or floor drains? Here's how to get rid of drain flies in commercial kitchens, restrooms, and utility areas without overcomplicating it. This guide covers what causes drain flies, how to kill them quickly, and the best prevention methods for business owners and facility managers.

Step 1: Identify the source with duct tape.

Step 2: Scrub and flush drains with boiling water.

Step 3: Use DIY or commercial drain cleaners.

Step 4: Trap adult flies with vinegar or fly paper.

Step 5: Sanitize surroundings and prevent moisture buildup.

These steps help remove drain flies quickly and cost-effectively in kitchens, restrooms, and utility areas.

Drain flies—also known as sink flies, sewer gnats, or moth flies—breed in stagnant water and organic buildup in pipes. If you notice gnats coming from the drain, especially in high-use areas like commercial kitchens, restroom drains, utility sinks, and HVAC condensation areas, it’s likely due to:

• Biofilm and gunk inside drains
• Standing water in pipes or sump pits
• Leaky plumbing or HVAC condensation
• Poorly cleaned garbage disposals

Drain flies in bathroom or kitchen areas are a signal that it's time to deep clean your plumbing and eliminate excess moisture.

Here’s a step-by-step strategy to eliminate a drain fly infestation at your business.

1. Identify the Source of the Flies

• Use the duct tape test:
• Place a strip of duct tape over the suspected drain at night.
• Check for trapped flies in the morning.

2. Physically Clean the Drain

• Scrub inside the drain using a long-handled drain brush.
• Flush it out with boiling water to loosen organic debris.
• Repeat daily until the flies are gone.

Don’t skip this step! Most infestations come from deep inside the pipe walls.

3. Use a Natural or Commercial Drain Cleaner

For a DIY drain fly treatment, try this:

• Pour ½ cup baking soda (sodium bicarbonate) down the drain.
• Follow with 1 cup of apple cider vinegar.
• Let it sit for 30 minutes.
• Rinse with boiling water.

For larger infestations, use a non-corrosive commercial drain cleaner designed for food-safe environments. Avoid chemical drain cleaners that can damage pipes or cause health concerns.

4. Trap Adult Drain Flies

Use homemade drain fly traps like:

• A bowl with apple cider vinegar and a drop of dish soap
• Sticky fly paper or commercial traps placed near the drain

These traps won't kill larvae but will help reduce visible adult flies.

5. Sanitize Surrounding Areas

• Clean your sink, counters, and garbage disposals regularly.
• Address any leaks or condensation sources.
• Use drain strainers to catch food particles and debris.

Keeping everything dry and clean is key to stopping reinfestation.

These are low-cost, effective ways to get rid of sink flies and stop drain flies long term.

Do drain flies bite?

No. Drain flies don’t bite or sting, but they can spread bacteria from contaminated surfaces.

Are drain flies harmful?

While not dangerous, they can raise sanitation concerns, especially in foodservice, healthcare, or hospitality environments.

How do you get rid of gnats in drain lines?

Use a mix of physical cleaning (brush and boiling water), natural enzymes, and moisture control. For severe cases, professional drain service may be required.

Can I prevent drain flies entirely?

Yes—with regular maintenance, proper drainage, and sanitation. Install drain strainers, keep floors dry, and flush drains weekly with boiling water.

You don’t need harsh chemicals or costly pest control to get rid of drain flies in kitchens, bathrooms, or industrial sinks. With consistent upkeep, a few natural cleaners, and smart traps, most infestations can be resolved in-house. If the flies keep returning, it may be time to assess your drainage layout or call a professional plumber.

Product Compliance and Suitability
The statements contained in this guide are intended for general informational purposes only. Such statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness, or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand, and follow all manufacturer instructions. Portions of this article were generated in part by ChatGPT, and edited by a member of the Zoro team.