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Holding Tank Sensor

One of the more common complaints we hear about RVs these days is holding tank sensor failure. Although not an earth shattering problem, it is a real irritant, nonetheless, especially for those unlucky enough to have a black water holding tank that's not located directly under the toilet. Not being able to see directly down into the tank has definite drawbacks.

The malfunction usually becomes noticeable when waste water starts backing up into the toilet, sink, or shower, but your gauges show that the tank is only a quarter full. Yuck! Aside from cleaning up the disgusting mess, the problem is usually relatively easy to diagnose and correct.

The problem is either mechanical, electrical, or the result of a dirty in-tank sending unit. Here's a good, inexpensive way to find out if a dirty sending unit is indeed the culprit, and most times fix it if it is.

The next time you put your RV up between trips make sure you've emptied and thoroughly rinsed the holding tank. Then fill it with fresh water to nearly full, add the correct amount of an excellent quality bacteria type liquid holding tank chemical for the capacity of the tank, and fill it the rest of the way with water. Let the RV sit as long as you can without adding anything to the tank. This will allow the bacteria and the enzymes they produce to do their job of digesting any toilet paper or organic debris that may be clinging to the sensors.

Finally, before your next outing, simply empty and thoroughly rinse the tank once again. If you have allowed sufficient time (a week or so should do it) for the product to work the sensors should read correctly. If all else fails you'll have to take the RV to a service center for additional diagnosis and repair.

We also recommend that this procedure be performed on an annual basis to keep both your grey and black water holding tanks, sensors, and dump valves pristine clean. At about a dollar  to treat a 40 gallon holding tank, this is the least expensive insurance you'll ever buy. Remember that extremely dirty holding tanks didn't get that way overnight. Be sure to allow the enzymes enough time to 'eat' their way through all of the accumulated crud.

Regular use of a high quality liquid enzyme producing bacteria type holding tank chemical, along with proper holding tank dumping techniques, should prevent any reoccurrence of fouled holding tank sensors.

Okay, now you ask, what IS the 'proper' way to dump your holding tanks? Here's what we recommend. Empty the holding tanks when near full by first dumping the black water tank and then, after it's drained and with the black tank valve still open, the grey water. When all the sewage has drained, close both valves.

You'll want to rinse out the sewer hose before storing it but, if using a good liquid bacteria holding tank chemical, will be pleasantly surprised at how clean it is even before it's rinsed. As for rinsing out the tanks after draining, well, our customers tell us they usually don't have to. Again, if using a quality product, the contents of the tank will be almost completely liquid and will empty fast and clean.

We also suggest that you add a couple of gallons or so of water and the appropriate amount of chemical to your empty holding tanks before storing your RV. The chemical will continue cleaning your tanks and you'll be ready to go without having to worry about that minor chore before your next outing.

If you can gain access to your tanks you can determine their capacity with the following simple formula. All measurements are in inches.

    L x W x H divided by 231 = capacity in gallons.

    Example (my fresh water holding tank): 50" x 21" x 16" = 16,800 divided by 231 = 72.72 gal. capacity (close approximation).

Dirty sensors can give false reading, not only showing fuller than they really are but under reporting as well.


I bought and use the Flo-Jet Waste Water Pump kit and I LOVE IT! No more waiting at the dump station or paying fees to dump or finding an open dump station. I simply connect the portable pump, run a small diameter hose to my homes sewer clean out and press a button. Problem solved. Read more at: Flojet RV Waste Water Pump Kit

See also Holding Tanks

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