Originally Posted by tloynd
The underside is sealed. Where are these four wires you speak of? Yes to the first question. It seems to have stuck after the very first fill up. It was very full though.
There are 4 probes into the tank. Bottom (common), 1/4, 1/2 and 3/4. [Wait, there may be a 5th at full]. Each probe sends a very small signal (conductivity of the grey water) back to the control box.
With the enclosed bottom, you won't be able to service the wires without dropping the plastic.
With the tank empty, you may be getting a reading from just the damp walls. Once 2 probes are under water, you may start getting accurate readings.
Have you checked the readings as the tank is being filled for flushing?