How to Get Rid of Sump Pump Flies: DIY Guide

Name: I have flies coming into my basement form sump pump system.
Uploaded: 2026-02-21
Duration: 2 min 37 s
Description: Discover proven, practical steps to eliminate sump pump flies. Learn detection, cleanup, safe treatments, and prevention to keep your basement dry and pest-free.

Discover proven, practical steps to eliminate sump pump flies. Learn detection, cleanup, safe treatments, and prevention to keep your basement dry and pest-free.

Sump Pump Check Team

February 21, 2026·5 min read

Sump Pump Basement Drainage Maintenance Drainage

Quick AnswerSteps

To get rid of sump pump flies, clean and rinse the sump pit, remove slime and organic buildup, and improve drainage around the pump. Unplug the unit before cleaning, wear gloves, and reseal the pit cover to prevent reentry. According to Sump Pump Check, most infestations start with organic film in the pit and clogged discharge lines.

Understanding Sump Pump Flies

Drain flies, also known as moth flies, are small, fuzzy insects that thrive in moist, organic matter. In homes with sump pits, these flies often breed in the slimy film that can form on pit walls, the surface of standing water, and in clogged discharge lines. The life cycle from egg to adult is quick in warm, damp conditions, so a single clean-up can reduce the population substantially—but only if you address the root causes. A clean pit prevents larvae from feeding on biofilm, while a dry environment hampers adult flies from laying more eggs. For homeowners, the most effective approach combines mechanical cleaning with safe pit maintenance. The Sump Pump Check team emphasizes that addressing both moisture and debris is key to long-term relief, rather than relying on one-off treatments.

Brand note

According to Sump Pump Check, infestations frequently trace back to organic buildup inside the sump pit and along the discharge path. A thorough cleanup coupled with preventive maintenance dramatically lowers the chance of a recurrence.

Identification tips

Look for wispy, moth-like flies hovering near the sump pit or around the discharge pipe. If you see sudden spikes after heavy rainfall or rapid snowmelt, the pit may be collecting more organic debris than usual. Check for standing water, slime, and a musty odor—these are signs the biofilm habitat is active. Document where you see the most activity and plan to clean those areas first. Regularly inspecting the pit cover and surrounding seals helps catch problems early before a full infestation develops.

Tools & Materials

Protective gloves(Nitrile or latex; long sleeves recommended)
Safety goggles(Eye protection to guard against splashes)
Bucket(For collecting debris during cleaning)
Stiff brush / scrub brush(For scrubbing pit walls and pump housing)
Sponges and rags(For wiping surfaces and drying)
Old towels(Lay on floor to absorb spills)
Long-handled cleaning brush(Useful for hard-to-reach areas)
Flashlight(Inspect the pit and discharge line closely)
Garden hose or utility sink hose(Rinse pit after scrubbing)
Enzyme-based drain cleaner(Safe for septic systems; follow label directions)
Hydrogen peroxide (3% solution)(Alternative biological cleaner; avoid mixing with bleach)
Baking soda(May help in neutralizing odors when used with hot water)
Plastic trash bags(Dispose of debris securely)
Sump pit cover or screen(Keep pests out between cleanings)

Steps

Estimated time: 60-90 minutes

1
Power down and prep the area
First, unplug the sump pump and switch off the electrical circuit to prevent any risk of shock. Move any nearby items so you can access the pit from the top. Put on gloves and goggles to protect your hands and eyes from grime and contaminants.
Tip: If you have a backup pump, keep it handy but do not run it while you clean the primary unit.
2
Remove standing water and debris
Use a bucket to scoop out standing water and remove visible debris from the pit. Clear away sediment, algae, and any organic matter clinging to the pit walls. The goal is to reduce the food source for fly larvae and expose biofilm that supports growth.
Tip: Dispose of debris in a sealed bag to minimize odor and contamination in your living space.
3
Scrub the pit walls and pump housing
With a stiff brush, scrub all interior surfaces of the sump pit and the exterior of the pump housing to loosen biofilm and slime. Focus on corners and the bottom where organic matter tends to accumulate. Rinse with your hose frequently to remove loosened material.
Tip: Keep the brush angled so you don’t push debris into the pump's intake.
4
Rinse and dry the interior surfaces
After scrubbing, rinse thoroughly with clean water. Allow the pit to dry as completely as possible before resealing. Dry surfaces reduce microbial activity that supports fly larvae.
Tip: Use towels to absorb excess moisture and speed up the drying process.
5
Apply enzymatic cleaner to disrupt biofilm
Apply an enzyme-based drain cleaner following the product directions. Enzymes digest organic film that serves as a food source for flies. Do not mix with household bleach or other cleaners, as dangerous reactions can occur.
Tip: Let the cleaner sit for the recommended dwell time to maximize effectiveness.
6
Rinse again and inspect for remaining buildup
Rinse the pit once more to remove any leftover residue. Inspect the pit walls, floor, and discharge path for any missed biofilm or slime. Address any stubborn spots with a repeat scrub.
Tip: Pay attention to the discharge pipe where blockages can form.
7
Consider a hydrogen peroxide treatment (optional)
If you prefer a second cleaning step, apply a 3% hydrogen peroxide solution to the pit and rinse after a few minutes. This is a less aggressive option than bleach and can help sanitize surfaces without harming the pump.
Tip: Avoid mixing hydrogen peroxide with enzyme cleaner or bleach.
8
Seal and protect the pit
Reinstall or replace the sump pit cover or screen securely to reduce future access by flies. Check that the cover fits tightly and that the seal around the lid is intact.
Tip: Add a simple screen over the discharge valve area if feasible to deter pests.
9
Test the pump and monitor the area
Plug the pump back in, restore power, and observe the system for a short run to ensure proper function. Over the next week, monitor for new fly activity and keep the area dry and clean.
Tip: Set a monthly quick-check routine to maintain a fly-free sump pit.

Pro Tip: Use enzyme-based cleaners to disrupt biofilm without harming the septic system.

Warning: Do not mix cleaners with bleach or ammonia; dangerous gases can form.

Pro Tip: Maintain a dry, clean sump pit by addressing leaks and keeping the cover sealed.

Note: A simple screen over the discharge can reduce new entries of flies.

Pro Tip: Schedule regular cleanings (every 3–6 months) to prevent buildup.

FAQ

What are sump pump flies and why do they appear?

Sump pump flies are drain flies that breed in moist organic matter around sump pits. They appear when there’s standing water, slime, and food sources for larvae. Cleaning and drying the pit disrupts their habitat and reduces populations.

Are enzyme cleaners safe for sump pumps?

Yes, enzyme-based cleaners are typically safe for sump pumps and septic systems when used as directed. They break down organic film without harsh chemicals that could damage components.

Can I use bleach to treat sump pump flies?

Bleach can be damaging to some plastics and pumps and can create harmful gases when mixed with other cleaners. It’s better to avoid bleach and use enzyme cleaners or hydrogen peroxide per product directions.

How often should I clean the sump pit to prevent flies?

Aim for a thorough cleaning every 3–6 months, or sooner if you notice new fly activity. Regular checks help catch biofilm growth early.

What maintenance helps prevent re-infestation?

Keep the sump pit covered, fix leaks around the pit, ensure the discharge line isn’t blocked, and maintain a dry environment around the pump area.

When should I call a professional?

If flies persist after cleaning, or if you notice electrical issues, persistent odors, or mold growth, seek professional help. Professionals can assess underlying plumbing or drainage problems.