Fresh water tank fill issue

Avion, when the tank is full, water comes out of an overflow tube beneath the camper next to the drain tube/valve. Travisc, your suggestions are the only ones that have come up with as well. I was contemplating removing the check valve, or I'll have to be able to pressurize the water with an external pump. I asked the dealer about this issue, and he said that the check valve should be easy enough to open that simply pouring water through a funnel would create enough force to push the check valve open. Needless to say, I tried it and water just sat in the funnel.