Leak from top of black tank

awesomeman wrote:
Ok. How does a check valve at fill in leak onto the top of the black tank on the other side of the rv. Not debating. Just have no clue. Lol. Thanks guys

Water runs down the tubing from the water inlet, along whatever, and eventually drips down onto the black tank. Maybe it drips onto the black tank on the side nearest the inlet and flows across the tank.

It's also possible that something else is leaking and dripping onto the tank, though that seems a bit less likely since it doesn't happen when using the tank and on-board pump. Perhaps if the city water pressure is substantially higher than the pump water pressure it could be sufficient to make a loose fitting leak that otherwise stays dry.