yes to everything...if it is "stock". thing is, on a trailer this old, any number of things could have been changed.
there isn't a "valve", per se, that fills the on board water tank; its just a filler neck, like the gas tank of your car. Water supplied from the tank is pumped into the water supply lines; the pump creates the pressure, and a pressure sensitive switch turns it on and off.
water is prevented from shooting out the city water connection by means of a one-way check-valve. An identical check-valve is on the other end of the line, between the pump and the tank, thus keeping city water pressure from filling the tank.
the water heater "may" have had a bypass kit installed, which cuts it off from the flow of water in the winter. This enables the owner to pump antifreeze into the water lines, without filling the tank. (the tank can be emptied, so there's no need for freeze protection...but without a means of isolating it from the lines, one would need much more antifreeze to winterize the system.)
'73 Safari 23'
'00 Dodge Ram 1500 4x4 QC