Roy,
He said, with respect to the fresh water tank fill, "This camper has a connection that you screw the hose into just like the city water connection has. But the problem is, there is a check valve ." which suggests that in addition to his city water connection he has a fresh water fill connection that is also screw on, and also has a check valve. IOW, the way I read his post he has what amounts to two city water connections - one conventional one and one that is used to fill the FW holding tank. If that is the case the latter one would be a design SNAFU in my opinion.
OP is asked to clarify.