What Is The Best Way To Rinse An RV Black Water Holding Tank?

An RV black water holding tank is a part of your RV that definitely needs attention to ensure that everything continues working correctly. Here at the Line of Doody, we have all sorts of recommendations about caring for your black water holding tank, one of which is to rinse the tank after every dump if there is no line at the dump station. The reason why you want to do this is because even when using a high quality holding tank treatment, waste and paper have the ability to migrate to unexpected areas.

These include the ledges that allow the holding tank to sit in between the RVs frame rails as well as corners and along the sensor array. But since RVs can have many different types of equipment with many different setups, what does that mean? In this article we will cover various methods for rinsing a black tank. We will let you know our favorite method at the end of the article!

Built-In Tank Rinsing System

Many RVs come with a black tank rinsing system as standard equipment (Original Equipment Manufacturer, or OEM). This style of tank rinser can also be installed as an aftermarket kit and will function the same way as an OEM tank rinsing system.

These systems operate by attaching a garden hose to a fitting on the exterior of the RV. NOTE: We highly recommend that you use a dedicated hose for this style of rinsing system, in case the back flow preventer built into the garden hose fitting fails. If this were to happen, it would be possible for the liquid from the black water holding tank to make its way into the hose, which would contaminate the hose and make it unusable for any other purpose. 

Depending on the design of the black tank rinsing system that you have installed on your RV, the tank rinsing system may function in a few different ways. Some have spinning heads that look very similar to a sprinkler when operating.

Others have small holes cut in the head that allow water to spray at different angles. In either case, the rinsing system relies on the water pressure provided by the water source you are connected to. 

We have tested tank rinsing systems installed on black tanks (using a borescope camera to view the operation) and set up outside of the black tank. As we viewed the effectiveness of the spray pattern, we determined that even with ideal water pressure, these rinsers do not do a very good job at hitting every area in the tank.

Because of this, we recommend running your rinsing system with the black water holding tank valve in the closed position. Be forewarned that there may be stickers on your RV and cautions in the owner’s manual stating that this is not a good idea.

The reason for these warnings is that the manufacturer is trying to protect against possible damage to the RV as well as attempting to limit their liability if you happen to overflow the black tank. Their theory is that a full black water holding tank has the potential to break free from the frame rails and separate from the RV. This is not very likely, especially when the RV is sitting idle while you are rinsing  the black tank. 

The benefit of keeping the black tank valve closed is that it allows the water to fill up the holding tank rather than letting it drain out immediately. When you allow the tank to fill, the water level will rise and reach areas that may be missed by the spray pattern of the tank rinsing system, such as the ledges that allow the tank to rest upon the RVs frame rails. When the tank is full and you open the valve, you will be creating a much greater pressure force to break free waste and debris that may be stuck to the walls and floor of the tank, allowing for a deeper cleaning of the tank. The filling and dumping of the tank may need to be performed several times to make sure that everything has been cleared out of the tank. 

However, if you are uncomfortable with going against the manufacturer’s advice, we encourage you to operate within your comfort level and run the tank rinsing system with the black tank valve in the open position. If you do decide to leave the valve open while rinsing the tank, we recommend that you allow the tank rinser to run for around 20-30 minutes. This will give it the best chance to fully clean the tank.

Tank Rinsing Wands

For RVs which do not come equipped with a built in tank rinsing system, there are aftermarket tank rinsing wands. There are two styles of wand to select from; you will want to choose based on the plumbing layout of your RV. For RVs that have anything other than a short, straight pipe connecting the toilet to the black tank, you will need a flexible style swivel wand.

These rinse wands are much longer and have flexible or bendable sections which will allow them to be pushed past the 45 degree elbow(s) that connect the plumbing to the black tank. (You may need to use some force to get it all of the way down into the tank past all of the fittings.)

Once the head of the rinse wand makes it into the tank, the spinning head will spray the water out and into the tank, relying on water pressure to move the water around the tank. Because the water direction and angle are not able to be directed by the operator, it is a good idea to leave the black tank valve in the closed position in order to allow the water to fill the tank (similarly to the built-in tank rinsing systems).

When you are rinsing the tank for the first few times, it is helpful to have someone monitoring the sensor array at the control panel in order to tell when the tank is full. 

For RVs which have a toilet that is plumbed with a short, straight pipe run to the holding tank, you can use a single point of spray wand.

This style of wand is one of the most effective ways to rinse the black water tank, because you can control the direction of the water flow. When you are operating this style of rinse wand, it is a good idea to establish a pattern that you can repeat in future rinsing. Starting at the 12 o’clock position, as you are looking directly down into the toilet, slowly move the wand up and down,  pausing in between the movements to allow the water to blast the area directly with water. Move the wand clockwise to the different numbers that would be on a clock face,  repeating the motion and pausing until you return to the 12 o’clock position. It is best to use this style of rinse wand with the black water valve open since you will have the ability to control the direction of the water and focus the spray. 

Reverse Flush Valve Rinsing Devices

For this style of tank rinsing device, we recommend purchasing one with a knife valve built in, which will allow for the holding tank to be closed off while the valve is filling the tank. Keep in mind that the problem with this type of rinsing device is that the plumbing layout at the discharge manifold of most RV holding tanks will not allow for the water to be directed into the black water holding tank. Because of this the black tank will slowly fill with water.

And if you have a back flush rinsing the device without a knife valve built in, the water will most likely not make it into the black tank very far beyond the discharge port.

Rinsing the Black Tank Without Additional Equipment

It is possible to rinse out your black water holding tank without needing to purchase any auxiliary rinse wands or back flush devices. You will want to start by closing the black tank valve, then fill the holding tank completely full with water.

You can use a garden hose to fill the black water holding tank rapidly through the RV toilet or you can hold the toilet flush pedal down and slowly fill the black tank.  Next, open the black tank valve to let all of the water rush out of the tank. If you choose to use a garden hose, we recommend using a hose that you have dedicated to this task alone in case the hose falls into the black tank and hits the floor of the tank, becoming contaminated.

If you choose to fill the black tank by holding down the toilet flush pedal, we recommend doing so when you are connected to a water supply source with good water pressure, rather than pumping water from the freshwater tank.

The reason for this is that most RVs have only a 3-5 gallon-per-minute water pump, which  is relatively slow compared to the water pressure provided by a city water connection. In either case, it is advisable to leave the black tank valve in the closed position so as to allow the water to fill up the tank so that the water reaches all parts of the tank. As with the previous examples of filling the tank and letting the water rush out, this may need to be repeated multiple times in order to fully clean the tank out. And by the way, this is our personal favorite method to rinse out the black water holding tank. Having tested nearly all of the devices available on the market, we have found that since it is impossible to see inside the tank while using a wand or other rinsing system, fully filling and dumping the tank yielded the cleanest tank.

The Takeaway

Rinsing out the black water holding tank is a necessary part of maintaining a problem-free black water system. Fortunately, there are many ways to rinse the holding tank in order to keep it free from waste and paper buildup inside the tank. No matter which way you choose to rinse your black water holding tank, we recommend rinsing your tank after every time you dump its contents if possible. If that is not possible, due to a line behind you at a dump station, then we recommend rinsing the tank the next time you dump.

We also recommend that you rinse your tank when you are at a campsite at a full hookups campground, unless if you have a drain cleanout for your septic tank and you can legally dump your holding tank into it. This will help you avoid long rinse times at a dump station, especially if there is a line.

When you are rinsing your black water holding tank, it is helpful to have a clear elbow or sight glass fitting connected to your sewer discharge hose in order to monitor the water clarity and what is being rinsed from your tank. This will help you know when you have fully rinsed all of the waste and paper from the tank. We hope you learned something from this article! Happy camping!

Got a question you’d like answered by our certified RV technicians? Submit your question here!