Over time and with regular use, your RV holding tanks can build up sludge on the inside walls, which often causes false readings on the panel. You may have just emptied the tanks, yet the reading on the panel still shows that they’re full. Regular cleaning of the holding tanks can help to minimize this problem. If cleaning the sensors doesn’t help, you might consider replacing the sensors, which are usually nothing more than a kind of screw inserted into the side of your holding tank.
Go outside the RV to where the holding tank is and push the handle on the holding tank shut-off valve to the closed position. Double-check that the opening is closed by looking at the opening and even pushing again on the shut-off valve handle. If something is lodged in the shut-off valve, you might have to open the valve and then close it several times to get it tightly closed.
Fill the holding tank to where the reading on your panel reads “Full.” Run cold water at a medium speed in both the kitchen sink and in the bathroom at the same time. Keep a close eye on the level of the water inside of the holding tank to avoid any overflow. Remedy any inaccurate readings by looking through the toilet. As the holding tank fills, the water inside rises up to the tube in the toilet opening, which can take up to 20 minutes depending on the size of your tanks.
Open the holding tank shut-off valve from the outside of the RV once the holding tank has filled to the “Full” mark. Empty the tanks. Adjust the sewer hose to make sure it empties the tanks efficiently as the water pressure will cause the sewer hose to move about wildly like a snake.
Close the holding tank shut-off valve. Fill the tanks to the “Full” mark by turning on the cold water faucet to a medium flow in the bathroom and in the kitchen. Check the level of the holding tank frequently by looking at the panel or looking through the hole in the toilet. Once it’s full, open the shut-off valve outside the RV. Let the water completely drain, which can take about five minutes depending on the size of your tank. Make sure that the shut-off valve closes tightly as toilet paper can get stuck in the opening causing it to be lodged open.
Check the readings on your panel. Repeat this process again, if the readings on your sensors are still inaccurate add some natural bacteria eater and let it sit overnight with the water filled to the top.
Flush With A Wand
Use a wand, which is a three foot spray like extension, to clean the inside of your holding tank. Walk inside your RV with a garden hose to measure the length of hose you’ll need for this job. Go back outside and attach a wand to the end of a garden hose. Turn the water on outside to make sure there aren’t any leaks. Tighten or readjust the wand until it is tightly attached to the hose. Bring the garden hose back into your RV with the wand attached to it into your bathroom.
Recruit an assistant to hold your toilet open while you spray around inside of the tank with the wand. Spray around inside of the toilet making to spend a good bit of time around the sensor attachment area, which is usually toward the center of the RV. Exact placement of your sensors can be found by going underneath the holding tank outside of the RV. Find the holding tank, which is the large squarish tank attached to the shut-off valve. Throw a blanket onto the ground underneath the RV and visually look at the tank. The sensors are generally toward the inside of the RV where the electrical wires are hidden. Look for wires attached to the tank and you’ve found the sensors, which usually consists of three wires on one side and one wire about a foot from the three wires.
Finish cleaning the tanks with the wand. Check the readings on your panel. If they aren’t reading accurately, then clean some more.
Take the garden hose with the attached wand back outside the RV.
RV Probes: How It Works
Woodalls Forums: Removing Holding Tank Sensors To Clean Them?
I RV 2: Plan To Clean Black Tank Level Sensors