Sludge and soap residue build-up on the sides of RV black and gray water tanks can lead to false readings. The sludge acts like a conductor between the positive content level sensors down the tank to the negative probe that is located at the bottom of the tank. This will trigger the indicator panel to show that there is liquid level in the tank even when there is none. Horst Miracle Probes are considerably longer than standard probes and the sensor is surrounded by a Delrin body and Teflon tube which prevents any liquid residue or sludge from setting up a conductive path. The black tank probes have a specially designed “roof” over the probe sensor to prevent toilet paper from coming into contact with the probe and creating a false probe contact and related reading.