RV Waste Tanks: How to Avoid Inaccurate Monitor Readings

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Over time the walls of your RV waste tanks can get a build-up of sediments, which can falsify the sensors on the side of the tanks. Inaccurate readings caused by residue and stuck toilet paper on the walls of the RV waste tanks is a common problem owners regularly face.

Most systems have a main probe on one side and three or four several inches to the side. As the fluid level rises inside the tank, low voltage passes through to the other probes and indicates the various levels. When residue builds up on the sides of the walls, electrical continuity is still present so the probes send as if the tank is full when it is not. Even after completely dumping the RV waste tanks, you can still get a false reading from left over residue and items stuck to the walls where the probes are coming in.

If you are getting false readings, there is an inexpensive and easy way to conduct a quick cleaning of the black water tank walls. Take four to five of the five-pound ice cube bags and dump them down the toilet. The ice cubes will bang around the tank cleaning the sides and probes before they melt. Make sure to do this while driving, otherwise it will not be effective. The longer you drive the better. Once done, the water can be dumped down into a dump station.

Using ice cubes is a quick and easy way to clean residue off the side walls of your RV waste tanks. Hopefully doing this will take care of the false readings you are getting without having to spend a lot of money on replacing the probes. However, if cleaning does not work, it may be best to contact a certified mechanic.

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4 Responses to “RV Waste Tanks: How to Avoid Inaccurate Monitor Readings”
  1. Tom

    I guess that you don’t have a “macerator toilet”. Ice might not pass through too well!!!

  2. Mike Greene

    Any idea on where to find a wiring diagram for these probes? I have a mid 2000 fleetwood wilderness that my dogs decided they liked the taste of. Can’t seem to find anything online. Thanks

    • Customer Service

      Hi Mike. Thank you for visiting the RV Repair Club site and the opportunity to assist with your waste water issue. Finding a wiring diagram for a Fleetwood Trailer built in 2000 is almost impossible as you have found, unless you can talk a dealer into making a copy. The trailer division did not document very well back then and the company has since been sold and the trailer division closed. However, you should be able to repair your wiring system as they used a very similar process as most other manufacturers. At Winnebago we used one 16 ga 12+ wire (purple) coming from the monitor panel to the lower probe and a 16 ga 12 v- ground wire ()green) to the tank ground. The lower probe then had a probe positioned across and then purple, yellow, and blue wires ran from the three going up for 1/3, 2/3, and Full back to the monitor. You should be able to see what color wire is on the main probe and replace it back to the monitor panel.

  3. Roland Doucet

    You can also use water softener salt as it will not dissolve as fast and slosh around for a longer period of time. They are also environmentally friendly as it’s just salt in a compressed format.


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