How to test holding tank sensors

[Jbmsr]

My One Place external holding tank sensors manufactured by Precision Circuits Inc. worked great for the first year. My black tank recently started showing 1/3 even when empty then 2/3 too soon and for quite some time before reading full. I flushed my black tank with dawn, then Thedfords eco black tank cleaner at 400%. Each time letting it set for 24 hours and driving before dumping and flushing. No luck! Must be a bad sensor. I removed the two screws holding the black tank flush connection to see the 3 sensors. I used a long screw driver to reach in an touch each one. I wet my hand and touched the metal part of the screw driver to ground out each sensor while looking at the display. Touching two of them would change the display and one would not. Ok I knew I had a bad or blocked sensor. At dusk dark I used a very bright led pen with 6 LEDs and held it up behind the black tank and it made it transparent even with water it it. The attached photo's explains it all.

I cannot put ice in the tank and drive around. Thedford said that I would damage the electric toilet internally.

I will follow up with the rest of the story.

This is me trying to pay back to the forum. I am sure many know much more than me.

Thanks

Jesse