From what I can gather you were filling the fresh water tank and when it was full got a little water out the fill port? If this is correct I would check the fill port for leaks inside the camper, I can see mine if I remove a panel on the front of the sink base. Mine also has a vent line that comes back to the fill port from the fresh water tank, screen area built into the fill port housing. Is your vent line from the fresh water tank leaking or not connected to the fill port?
2017 Dutchman Denali 287RE
2017 Nissan Titan XD diesel