How do my RV’s tank sensors work?

It’s no wonder your tank sensors are the top frustration of your RVing experience. Almost no RVer’s tank sensors work, almost from the first couple of times you use your RV. We’ll get into why that is later (and what you can do about it!), but for now, let’s talk about how they work.

RV tank sensors come in two main types: probes and electronic strips. Most RVs have the probe type which are small metal nubs protruding into each holding tank (yes, your freshwater tank has them too!). 

Most often, there’s a solitary nub on side of the tank and a stacked array of them on the other side. In this type of sensor, an electronic signal is sent through the solitary nub, which travels through the “liquid” in the tank, and creates an electrical connection with the corresponding nub on the other side of the tank. The higher up the nub in the array is activated, the fuller your holding tank is.

The strip-type sensor uses what might be best described as a type of sonar or electronic pulse which measures the fullness of the holding tank. These types are most common on higher-end motor coaches and can go by the name SeeLevel (though there are other types, including Winnebago’s proprietary system).

Tank sensors fail for many reasons, the most common of which is that “stuff” gets deposited on the nubs and prevents accurate capacity readings. Although far less common for strip-type sensors, thick, sticky build-up in the tanks (especially the black one) can prevent accurate readings as well.

So what causes that build-up in your black (especially) and gray holding tanks? Almost always, it’s the enzyme, biological agent, or chemical tank additive you are adding to those tanks. Those additives are dissolving the tank’s contents (feces, toilet paper, etc.) – as they claim they will – but they dissolve into a thick, sticky slurry. That thick mixture is coating the insides of your tanks and fouling up those tank sensors (or the ability of the strip type to get accurate readings).

The solution? Get your holding tanks professionally cleaned, stop using those harmful tank additives, and start using much more water and, if you want, a tank solution like Kleen Tank’s Calgon-Pine Sol recipe.

In some cases, sensors will fail because of corroded wiring, failed electronics, or just too much hard, mineral build-up on the sensor nubs. A professional cleaning will get them working in 9 out of 10 times, but there’s no guarantee short of complete replacement.