Imagine you are traveling in an RV on a road trip. A beautiful mountain range, lush green trees, and natural beauty surround you. Taking a bathroom break is now necessary. You are welcomed by a huge swarm of flies when you enter the bathroom of your RV. 

This is not only disgusting but very irritating as well. You do not know where these flies are coming but you know one thing they are becoming a source of constant disturbance and irritation for you. Your road trip can be ruined due to the presence of these flies in your RV toilet.

Though these tiny creatures are a real problem, the good point is that you have many easy methods and techniques to get rid of them.

However, to get rid of them completely, you first have to find out their cause and how they reach inside your RV toilet. After that, it will become easy to select the method that will be effective to get rid of them.

Sewer Flies

Sewer flies are also sometimes known as drain flies. They are black. These flies spend most of their time on walls or ceilings. They like an environment full of moisture. That is why they usually live in sewers, drains, shallow water with scum, and septic systems.

The larvae of sewer flies remain in the water all the time. Their food is organic matter. They grow on that organic matter which they consume as food.

A drain fly or a sewer fly is a source of irritation and it can bring down your mood as well as your traveling spirit. Though these tiny creatures do not pose much harm to humans, still they are a source of spreading germs and bacteria. They are not known for spreading diseases in humans but they look nasty.

Identifying Drain Flies

Some features of drain flies or sewer flies are given below so that if you encounter any of them inside your RV, you will be able to identify them.

  • Fully grown adult sewer flies are 1/5 to 1/6 inches in length.
  • They are black, grey or dark brown.
  • Adult flies have wings. Their wings are covered with fuzzy hair.
  • Sewer flies have a moth-like appearance. You often misunderstood them as moths.
  • They have an antenna on their head.
  • They have a lifespan of 8-24 days.
  • They can lay more than 300 eggs in less than 48 hours.

How to tell if there is a Fly Infestation in your RV?

If you see sewer flies in your RV toilet regularly, then this is a clear sign that your RV has been infested by these flies. You should take immediate action when you see these in your toilet or bathroom. The female sewer flies can lay 30 to 100 eggs at a time. It takes 32 to 74 hours for these eggs to hatch.

Causes of Sewer Flies in RV

The RV has holding tanks that are used for holding wastewater from toilets, sinks, showers, etc. There are two tanks in your RV for holding wastewater.

One is the black tank that is used for holding everything that goes down into your toilet. The other one is the grey tank. This tank contains wastewater from showers and sinks etc in your RV. These tanks are the breeding ground for sewer flies.

The waste and dirty water in the black tank is the ideal place for sewer flies to breed and grow. You connect your RV to a sewer hookup to do dumping of waste; these flies get into the tank through sewer hose pipes. If you leave your grey or black tank valves open, then they also make their way into your RV tanks.

Once they enter the tanks, it is not difficult for them to make your tank their new home. The inside damp environment of your RV black tank is ideal for the sewer flies to grow and breed.

Once they start breeding in the tanks, it becomes very difficult to eliminate them. That is why you should immediately take action when you see the infestation of sewer flies.

Methods to get rid of Sewer Flies

Though infestation of sewer flies in your RV toilet is a serious issue, we have you covered by several methods to get rid of them. Following are some methods that you can implement to get rid of these tiny, nasty creatures.

1. Flush Black and Grey Holding Tanks

Flushing or draining the tanks of RV is the first method that you can use to get rid of sewer flies. Chemicals like bleach etc are not found to be much effect on the larvae and sewer flies. That is why different methods to flush the tanks are used. Some cleaning tools for RV tanks are given below.

  • Rinsing System: some RVs have built-in sensing systems that are used to clean and flush the holding tanks. These systems help to get rid of the sewer flies residing inside the tanks.
  • Dual Flush: this system has a hose pipe that is connected with the hose to spray water inside the tank. This is used to clear the sewer lines and clogged pipes. It has a powerful spray feature that helps to remove anything inside the tanks including sewer flies and their larvae.

2. Elimination of Breeding Ground of Flies

Once you have flushed and cleaned the tanks, now is the time to get rid of any remaining eggs or larvae inside the tanks. This can be done through any one of the following methods.

  • Use Bleach: some RV cleaning experts do not recommend the use of bleach because it can cause harm to the inside coatings and material of holding tanks. However many people use bleach to get rid of sewer flies and their larvae. You simply have to empty the holding tanks. Fill them with bleach and water mixture. Let it sit for a while, after that flush and rinse tanks properly.
  • Use Enzyme cleaner: sewer flies lay eggs in the organic film layer present inside the black tank. Enzyme cleaners attack directly on this organic film. This layer also works as a food source for the larvae. By getting rid of this organic film, you can easily get rid of eggs and larvae as their source of food will be no longer available therefore they will be forced to move away and find a new place.

3. Kill Adult Flies

Another way is to kill adult flies. This can be done by the following methods.

  • Flytraps: apple cider vinegar can be used to make a flytrap. It can be placed near the drain. The adult flies will attract it and will get killed.
  •  Insecticides: many insecticides are available that can be sprayed to get rid of adult flies.

Final Thoughts

Identifying and clearing the sewer flies at the proper time and by using proper methods is the only way to get rid of them. However, it may take different methods and several attempts to get rid of the sewer flies completely.


Why are flies coming out of my RV toilet?

The dump hose valves that you connect with the sewer hookup, make way for the flies to come inside the tanks. After that, if you leave your tank valves open, the flies make their way inside your RV toilet easily.

Sarah Michelle is a passionate writer and digital strategist interested in the evolving landscape of online content and user experience. Having closely followed the developments in digital marketing and search algorithms, Sarah brings a unique blend of insights into the marketing world and is committed to helping both creators and consumers navigate the digital realm with confidence.

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