In one of my rigs I could only fill with a water hose connected by screw fittings. There was no hose trough to just put the hose into. If yours is like that, there is a valve that you have to shut off that allows outside water to go to the taps and not to the tank.
If water still goes to the tank while connected, there is a check valve in the actual pump (you can't see it) that should prevent it.
Personally, I like to fill my tanks and run with the pump until it needs filling again. I do not like the constant pressure on the rigs pipes when I am away from it or when we are sleeping. Too many people have come home to burst pipes, just fill, use the pump when you need it, and shut off the pressure when you don't.
