City Water Connection FILLS Fresh Water Tank

[wanderlust]

Our first trip in over a year (rehabbing 2 knee replacements) to Salt Springs Rec Area. I hooked up the city water and the next day I noticed that water was dripping from the freshwater tank overflow; the tank was FULL. How did this happen? Is there a check valve somewhere that isn't working? Where can I find a "plumbing schematic" so I can understand the city/onboard water system?
Thanks in advance.
Bob

[Grumpy]

Sounds like some debris in the check-valve at the pump. Run it for a few minutes to clear it out. Not an unusual occurrence.