Fresh water tank fill issue

Cup fan wrote:
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.

There were two reasons I was asking where the overflow was. First, I would be very concerned if the overflow doesn't relieve as much water as the city connection can put into the tank, otherwise you can burst the tank. Second, if the overflow was large enough and high enough, I though that you may be able to use it as a secondary fill. It appears that this option will not work.