Tank gauges - how do they work?

Simplistic explanation;
*screws through wall of tank at various heights
*wire connected to each screw
*current passes through the water to connect the screws electrically and complete circuit.

I fixed mine. Only had to make one minor adjustment so far this year. If you read this thread you will find that I had nothing but negative response to any new ideas.

Thread

Wiring diagram of a common type:

Wiring

Simplest answer based on most of what I've seen on here is "poorly" :B

Most important thing to know about the gauges in the F/W, grey and black tanks is that they are notoriously INACCURATE....to the point of near uselessness. We picked up our brand-spankin' new TT and the gauge on the black tank read Full. Some folks have changed theirs to a brand that is supposedly better, but no info here on the brand or exactly how satisfied they are now. If you go into the members listing and look for Chuck_S, he made the change, believe he has pictures of exactly how he did it and all the info you'd need. He most often is on the hybrid side of RVNet. Others may have the same info.

Usually the F/W tank is pretty much correct. The grey is likely close, but the black tank is anybody's guess. The slightest piece of debris of any kind can make the sensors go crazy. Even a good flushing of the black tank can still leave just a speck of TP or other and it'll show an incorrect reading.

After some use, you'll be able to know about what level you're at with the grey and black. I found, nearly the hard way, that when the kitchen sink starts draining very slowly that it's likely backing up into the shower. Our system is to be stingy with water going into the grey tank and very generous with the water for the black. 3 - 4 days is about our limit on grey and that's with 2 of us.

I believe the "sensor" uses the liquid to close "the switch"... the same as those water alarms people place near water heaters. The problem is the "sensor". I assume this is just open conductors spaced apart. Any splash or high humidly would cause problems.

There is an aftermarket tank sensor system that I've heard is very accurate.