Well, I learned another new thing this week.
I have Horst Probes in my black water tank and my gray water tank.
Anyone who has them knows they work GREAT.
Horst tank Probe Installation
Suddenly my gray tank stopped indicating properly and I was devastated to say the least. It indicated full when empty; after cleaning 1/3; after a second cleaning 2/3; I was going crazy.
I tried everything with no consistent results.
Yesterday I removed the gray tank probes and found TP bits wrapped around the coil of the gray water probes.
HEAD SLAP! IDIOT!
Following the advice of a previous thread about NASCAR campers who added an end of mast shutoff valve to allow transfer of gray water to the black tank to extend stay times while boondocking, I tested it this summer and it worked as advertised. I was very happy.
Till this happened. HOW it happened I have no idea because the water should have flowed only from the gray tank into the black with mixing only in the black tank. That was the theory anyway. Most likely works fine with the button style probes; but the Horst "coil type" probe is unforgiving of solids and paper as it gets trapped in the coil spring and is very hard to clean.
Everything is back working correctly now; but what a learning experience!
If you will be using this "transfer" method and install the horst probes, use the black tank type in both; just in case.