Fruit flies in the drain areas of your RV can be a considerable hassle, and spoil your vacation. Worse still, it is not just fruit flies you have to worry about. There is also the risk of infestations from drain flies in your RV. If you have an infestation of some sort, it may well be originating from your portable black water tank.

Of course, a quick swat can disperse these pests, but they will soon be back. Therefore, it is crucial you find a more long-lasting solution. This article aims to inform you about how to get rid of fruit flies in drain areas of your RV.

Do You Have an Infestation of Drain Flies or Fruit Flies in the Drain Areas of Your RV?

Drain flies and fruit flies tend to be a lighter color and fuzzier than common house flies. Don’t be too concerned about precisely identifying which type they are. Indeed, you don’t want to get too close to these pests as they have come from your RV’s black water tank. Therefore, they are likely to be carrying all sorts of germs. 

A Bit More About Drain Flies

Fruit flies, drain flies, or sewer flies? Regardless of which of these pests has infested your RV black water tank, they are a significant hassle. However, they do not bite or sting, so that should be slightly reassuring. 

Drain flies are also referred to as moth flies, and this is because of how they move. Rather than flying, they have a bouncing motion about 2-3 feet above the floor. They also need to settle frequently as they tire quickly. Although they are attracted to light, when they rest it tends to be in shaded areas. 

You can use these habits to your advantage, For instance, using an electric fly-zapper to leverage the flies’ attraction to light. Of course, this attraction also results in you becoming bombarded with such pests. 

Although it isn’t pleasant to have them around, drain flies cannot harm you directly. However, as they originate from your RV black water tank, they can spread the dangerous bacteria that lives there. This bacteria is particularly dangerous if it ends up on food. In an RV, the kitchen is usually next to the bathroom, so drain flies do not have far to travel to land on your food. 

Drain Fly Life Cycle

Drain flies live and breed within decomposing organic material in your RV black water tank. Your portable gray water tank could also harbor these pests. Their life cycle starts as an egg, before developing into larvae, then fully-grown adults. 

This whole process can take just one week, but typically it’s between 14 to 21 days. After this time, they are capable of laying eggs. An RV black water tank provides the ideal living and breeding environment for these unwelcome visitors. Therefore, you can very quickly find you have a fruit fly or drain fly infestation on your hands. 

How to Prevent Drain Flies Infesting Your RV

All is not doom and gloom! The good news is, there are plenty of things you can do to prevent drain flies from infesting your RV. Let’s take a look at a few of them.

Check Your RV Hook-Ups

The first thing to do is check your RV hook-ups to ensure the valves are closed. You should only open the valve on your RV black water tank when you are emptying it. The reason for this is that the tank needs to contain water to avoid waste forming into a pyramid. If this were to occur, you would have a particularly nasty problem to deal with. 

Another issue of leaving the black tank open is that the odors are not contained within. Ascending odors will attract drain flies. Worse still, rats have been known to make their way up RV sewer hoses! Therefore, only open this valve when you are emptying the tank.

Although the issue is not as severe with gray water tanks, these too should remain closed until you empty them. 

Bleach Your Tanks

Bleach isn’t effective at removing drain flies from regular homes. That’s because there is no way of closing the pipes, so the bleach simply flows past the eggs and larvae. However, with an RV, you can close the waste tanks’ valves. Therefore the bleach will rise with the water level, eventually contacting and killing the eggs and larvae.

You should NEVER mix bleach with ammonia. The chlorine content in the bleach, mixed with ammonia, produces chlorine gas. This gas can be fatal in high concentrations or confined spaces. As a rule, only use bleach on its own, without any other chemicals, acids, or cleaning agents.

Dilute the bleach at a ratio of one ¼ cup of bleach to 1 gallon of water. This amount is suitable for every 15 gallons of tank capacity, so you should adjust according to the size of your black water tank. Larvae are more likely to amass at the top of the tank, so ensure you prepare a sufficient amount to fill the tank. 

Leave the bleach in the tank for at least 4 hours, preferably overnight. This period will allow the bleach sufficient time to penetrate the organic material film, destroying the eggs and larvae. After that, drain the tank and rinse it thoroughly.

Enzyme-Based Drain Cleaners

Another way to remove drain or fruit flies in drain areas of your RV is to use an enzyme-based cleaner. These cleaners focus on the organic material on which the flies live and breed. Therefore, they are particularly effective, as they leave the flies without a habitat. As they don’t contain formaldehyde, you can still empty your tank at an RV dump station. Atomic has several such products available. 

Also, these cleaners are easy to apply, and you simply need to pour them down the drain. Before you apply the cleaner, drain the tank as normal. Ideally, leave the cleaner in the tank overnight. Afterwards, drain the tank, rinse it, then rinse it again. 

You might need to reapply the enzyme-based cleaner several times to clean the tank sufficiently. You will know when it is clean enough as the organic material film will be removed.

Hot water can kill the useful bacteria, while cold water can restrict their effectiveness. Therefore, when diluting the cleaner, only use warm water. 

In normal daily life, the human body produces sufficient bacteria to break down fecal waste. However, considering we are talking about RV black water tanks, enzyme cleaners are an ideal solution. An added benefit of an enzyme cleaner is that it will remove odors while breaking down the organic mate film.

Manual Cleaning

Drain flies can be elusive, often breeding in the uppermost regions of the tank. People can miss these areas during their regular cleaning schedules. Before you clean the tank, inspect the pipe linking your sink to the portable black water tank.

You should clean these areas using a good-quality drain brush. Of course, this will require a bit of effort on your part! You should take care when using these brushes. Often, these RV drains have a waterless valve rather than a P-trap. Using a “snake” rod can damage these valves. Consider checking before you start brushing.

Something else to consider about such valves is that they don’t require antifreeze. As they don’t have any water, there is nothing to expand in sub-zero temperatures.

Also, if you use a drain brush, ensure you clear any lingering film from the pipes. Doing so is particularly crucial around the top of the tank, as bleach or enzyme-based cleaners will not reach these areas.

Removing Drain Flies From RV Gray Water Tanks 

Fruit flies and drain flies can originate from your RV gray water tank too. Although it isn’t as common as with black water tanks, you should be prepared to deal with this problem.

Generally, soaps and shampoos are quite effective in limiting organic material and sanitizing gray water tanks. Therefore, any drain flies entering your tank will find scant habitat for breeding and egg-laying.

However, they can still get inside. Consequently, you still need to remove them, and you can do this using similar methods as for your black water tank.


Drain flies or fruit flies in drain areas of your RV can ruin your vacation. Hopefully, reading this article has given you a few ideas of how to get rid of drain flies. If you need any more information, contact Atomic today.