It’s a common joke in the RVing community that the holding tank sensors are only accurate until you use the tank for the first time. If anything sticks to the sensor, it will give a false reading of being more full than it actually is. Sensors may indicate a nearly full tank even right after you’ve emptied it. When doing research for this blog post, we found that the sensors are placed in the lowest point of the tank. Where the heavier objects will set, stick to your sensors then giving false readings.
If your black water tank shows full when it is empty, it could be one of four reasons. The sensor could have built up debris, preventing an accurate reading. The tank could also have a pressure build-up because of clogged vents. You could also have a wiring issue or a faulty black tank sensor. More than likely what we’ve found is there is a build up of debris.
When a sensor inside the tank gets covered by food particles or toilet tissue it completes the circuit and relays the information to the monitor panel. It is possible for the holding tank to be empty but still register as 1/3, 2/3 or full because the tank sensor for a certain level in the tank is covered by debris. If the tank sensors are not displaying the proper amount of content in the tank you don’t know how much is in the tank until it is completely full. When the gray water tank is full, the the water backs up through the shower/tub drain. When the black water tank is full the wastewater come back up into the toilet. These are two problems all RV owners can do without.
There are a couple things we as owners can do to correct false tank sensor readings. We try to flush and rinse the black tank every time we empty it. You could use a flush that is built in the tank or purchase a wand that has a nozzle that sprays high pressure streams of water in every direction inside the tank. After we empty the tank, we flush the tank for several minutes. This cleans the tank sensors and helps prevent build-up on the sensors that can result in false tank readings.
Another method to clean tank sensors is to add a tank sensor cleaner to the holding tank after the tank is emptied. Add enough water to completely cover the bottom of the holding tank and add the sensor cleaning treatment according to the instructions. As you drive or tow the RV, the cleaner moves around and cleans the sides of the tank and the tank sensors. But if your not traveling, the sensor cleaning treatment will continue to work as the tank levels rise too.
Tip: Every time you empty the holding tanks add enough water to completely cover the bottom of the holding tank and then add the holding tank treatments. This will keep the holding tank cleaner and help prevent clogs and other holding tank related problems.