Bizarre holding tank problem! It fills up on its own!

usmohls2@yahoo.com wrote:
Do you have a pressure regulator on the hose from city water?

,
No. Could be pressure because it did this in Virginia and now Florida, but not in South Carolina. What would excessive pressure cause? Again, nothing going down the drains. The hot water pressure valve drains onto the ground. No gray water flush that I can find, no icemaker.

Maybe the RV is haunted. That's my guess. But I'll keep looking.