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Where Is The Sensor On RV Black Water Tank?

If you are new to the world of RVing, you'll want to quickly familiarize yourself with the ins and outs of the black water tank. Though no one enjoys emptying and cleaning this part, it's an important task that needs to be routinely done. If you are wondering where the sensors are for the black water tank, we can help you. We researched RVs in great detail so you'll know for sure where the sensors are located.

The RV black water tank sensors are located inside the tank. Most black water tanks will have two sensors located along one of the interior sidewalls of the tank. One will be located near the bottom, while the other will be closer to the top.

Now that we know where the black water tank sensors are located, we'll take a look at how they function. You might also be curious how you would replace a black water tank sensor or how these sensors can be calibrated. For the answers to these questions and more, read ahead in this post to see what our research has uncovered.

An RV dumping its black water tank on the drainage, Where Is The Sensor On RV Black Water Tank?

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What The Black Water Tank Sensors Do

The black water tank sensors provide an important service to you and your RV passengers. These sensors will alert you to different fill levels of the tank.

This way, you will be able to monitor how much room you have left in the tank, making it easier to plan when it needs to be emptied. They also alert you when it is nearing full so that the tank does not overflow.

No one wants the contents of the black water tank to begin to seep out of the tank and into the RV. Paying attention to the information these sensors provide is critical to your health and your comfort. But don't rely on the sensors alone.

An RV parked on a beach showing scenic view of the sunset

Sensors Can Become Obstructed

No system is perfect. Though the black water tank sensors are well designed and tested, they are subject to obstructions by the contents of the tank. If you don't clean the tank thoroughly, the sensors can have waste accumulate on them over time. This will keep them from working properly.

Using the wrong type of toilet paper can lead to this buildup as well. Be sure you only flush paper products that are meant to be used in an RV toilet, or you'll find that your sensors won't do their job.

If you don't use your RV toilet often, you should still have the black water tank emptied and cleaned at the end of each trip. If you don't, some of the waste left inside it will harden. This will possibly obstruct your sensors.

RV owner removing a cap from the RV sewage container

Sensors Can Malfunction

Sensors will fail over time. While they can be replaced, you will probably not be aware that they aren't working properly until you notice some signs of a full tank.

Whether your sensors are obstructed or failing, there are some telltale signs that your black water tank is getting full. If you notice any of the following, empty and clean your black water tank as soon as possible:

  • Your RV toilet is burping or bubbling after it is flushed
  • You notice the smell of sewer gas getting stronger
  • There is sludge beginning to seep out from under the base of your toilet

How Do You Calibrate A Black Water Tank Sensor?

Woman holding a hose remove sewer water from the RV

The sensors inside the black water tank cannot be calibrated. But the tank sensors' monitor can certainly be calibrated. This will ensure that it is displaying the correct information as relayed by the sensors.

To calibrate the sensor monitor, you will need a small Phillips head screwdriver. When you have emptied and cleaned the tank is the best time to calibrate. 

During your final rinse of the black tank, keep the tank full. Locate the set screw above the black water tank button below the monitor. Turn the set screw, and it will change the indicator light from "full" to "3/4." Move it back into the "full" position.

Drain the water you are flushing the black water tank with, and you'll see the indicator lights change until they say the tank is empty. Your sensor monitor is now calibrated.

Technician checking the RV computer date to check for any damages

How Do You Replace A Black Water Tank Sensor?

Hopefully, you'll never have to take on the task of replacing a black water tank sensor. These are embedded in the sidewall of the tank and are not the easiest thing to get to. But it can be done.

1. First, You Should Make Sure That The Black Water Tank Is Empty

You'll be removing the sensors from the sidewalls of a holding tank. These sensors act as plugs, so when they are removed, any liquid inside the tank will empty through the holes left by the removed sensor.

Be sure the tank is empty and clean before you go any further. Otherwise, you'll have a horrible mess to deal with.

2. You Will Need To Remove The Bottom Covering Of The RV

To access the tank, you'll need to remove the protective covering from underneath the RV. These are often held in place by compression nails, which means you'll have to carefully pry each of them out. Once the covering is removed, you'll be able to locate the black water tank.

3. Find The Black Water Tank

The sensors will be inserted into the sidewall of the tank itself. You will notice them protruding from one side, connected to wiring that connects the sensors to your tank sensor monitor. The sensors can be removed with a small wrench, disconnected from the wiring, and replaced with a new sensor.

4. Inspect The Sensors You Just Removed

If you notice a lot of buildup on the sensors when you remove them, the sensors might not be faulty. The buildup could be obstructing the sensors. You can then opt to clean the sensors and replace them. If they are not giving an accurate reading, then they should be replaced with new ones.

If you'd like a video tutorial on replacing the sensors on the black water tank, you can watch it below:

How Do You Empty A Black Water Tank?

You will empty the black and grey water tank at the same time. When you are parked near an approved tank dumping site, put on some rubber gloves and get the drain hose attached to the valve. Run the other end of the hose to the drain.

A man dumping waste water in his small motorhome to a designated dumping station

With the hose attached at both ends, open the valve to empty the contents of the black water tank. When it is empty, close the valve and open the valve for the grey water tank. This will help flush any leftover gunk from the black water tank out of your hose.

Close the grey water tank. Flush fresh water through the black water tank and out the hose so that the black water tank will get clean. Close the valves, put away the hose, and add an approved chemical to the black water tank. You're all done until next time!

Final Thoughts

An RV dumping its black water tank on the drainage

The black water tank sensors are tricky to find but can be accessed with a little bit of time. These sensors can get obstructed, rendering the monitoring system useless.

Keep your black water tank on a routine schedule of emptying and cleaning, and only use approved paper products in your RV's toilet. This will keep your sensors working like new.

We hope this post on black water tanks answered all of your questions. For additional information about this vital RV part, we suggest reading the following posts:

RV Black Tank Flush Not Working – What To Do

How Long Does A Grey Water Tank Last You Without Hookups?

How To Get Rid Of Sewer Flies In RV Toilets