How to Get Rid of Sewer Flies in Your RV

How Sewer Flies Get Into Your RV

Sewer flies do not appear randomly in an RV. Once they gain access through the plumbing system, they settle in areas where organic waste and standing water collect, such as black and gray tanks. These conditions allow them to breed and spread quickly throughout the plumbing system and the RV.

The most common ways sewer flies get into your RV include:

• Leaving black or gray tank valves open. Open tank valves give sewer flies a direct path from the sewer connection into your RV tanks. The flies can then enter the RV and lay larvae. If you have found fly larvae in your RV, this is why.
• Waste buildup in black and gray tanks. Residue that sticks to tank walls creates a food source where sewer flies can lay eggs. Infrequent or incomplete tank flushing allows this buildup.

Understanding how sewer flies get into your RV helps you stop the problem at its source. Once entry points are controlled and breeding areas are cleaned, getting rid of sewer flies becomes much more straightforward.

How to Get Rid of Sewer Flies in Your RV

To get rid of sewer flies in your RV, focus first on stopping their entry, then removing the organic buildup they feed on that allows them to reproduce. Surface cleaning is not enough. The entire RV plumbing system needs to be addressed.

These are the steps to eliminate sewer flies effectively:

• Keep black and gray tank valves closed. The first step is preventing sewer flies from entering the RV plumbing system. Leaving tank valves open gives flies a direct path up through sewer pipes and into the tanks. Only open the valves for dumping.
  
  
• Have tanks professionally cleaned. Over time, RV black and grey tanks naturally collect more than just liquid waste. Toilet paper, solid waste, grease, soap residue, and food particles can stick to the tank walls instead of draining out. As this buildup thickens, it can trap odors, cause slow draining, and lead to inaccurate tank sensor readings. In some cases, waste can harden into sludge, making normal dumping and rinsing ineffective. To properly remove this buildup, professional tank cleaning often uses hydro-jetting. Hydro-jetting involves directing high-pressure water inside the tanks to break apart compacted waste and wash debris off the tank walls and sensor probes. This process reaches areas that basic flushing can’t, helping restore proper flow and reduce lingering odors. After the buildup is broken loose, the tanks are fully filled and flushed multiple times. This final step washes out the loosened debris, ensures waste flows freely through the system, and confirms the tanks are draining correctly.

Once entry points are controlled and the tanks have been cleaned, you can focus on preventing sewer flies from reentering the system.

How to Prevent Sewer Flies From Coming Back

Preventing sewer flies in your RV comes down to consistent maintenance and proper plumbing habits. Once the system is clean, keeping it that way prevents future infestations.

These are the practices recommended to prevent sewer flies from returning:

• Keep black tank valves closed until dumping. Leaving the black tank open allows liquids to drain while solids remain, which leads to buildup and creates ideal breeding 
• Create a P-trap using the sewer hose. Creating a simple P-trap in the sewer hose helps stop this by using water as a barrier. To do this, set the sewer hose so it dips down and then back up before reaching the sewer connection. After dumping, let a small amount of water sit in the low spot of the hose. That trapped water blocks flies and helps prevent sewer odors from traveling back into the tanks.
• Perform regular tank flushes as part of routine maintenance. If your RV is equipped with a tank flush system, flushing after dumping helps prevent waste from sticking to tank walls and reduces organic buildup that attracts sewer flies.
• Use enzyme treatments for ongoing maintenance. Enzyme-based RV tank treatments help break down organic material before it can accumulate and stick to the tank walls.
• Schedule professional tank deep-cleaning on a routine basis. Having black and gray tanks professionally cleaned every year helps remove hardened waste and bio-film that routine maintenance can’t reach, reducing the chance of recurring sewer fly problems.

Consistent maintenance is what keeps sewer flies from becoming a recurring issue. When the RV plumbing system stays clean and properly sealed, flies have nowhere to enter or spread.

When Professional Tank Cleaning Is Recommended

Professional tank cleaning is recommended when sewer flies keep coming back despite regular flushing and enzyme treatments, or when black and gray tanks have heavy waste build-up that standard RV maintenance can’t fully remove. Recurring infestations and persistent tank odors are usually signs that waste has hardened on the tank walls.

I recommend having RV tanks deep-cleaned about once a year, or sooner if sewer fly problems don’t resolve with normal maintenance. This process removes hardened waste and bio-film from inside the tanks, eliminating breeding areas and helping restore proper tank function.

Conclusion

If you’re dealing with sewer flies in an RV, it’s a sign that flies have entered the plumbing system and found organic buildup and standing water inside the tanks. Getting rid of sewer flies means keeping tank valves closed, cleaning black and gray tanks, and removing the conditions that allow them to breed. Regular maintenance and proper dumping habits help prevent sewer flies from coming back, while periodic professional tank deep-cleaning removes buildup that routine care can’t reach. With the right approach, sewer flies in an RV can be eliminated and kept from returning.