Our MH has only one fresh water fill, that a hose attaches to. there is a valve which selects whether it is connected to the water lines, or to the fresh tank fill. There is no other way to fill fresh water by gravity. Water will come out an overflow when it is full, but better is to watch the gauge inside until it indicates full. The overflow line is not real big, and I don't like to fill it that full as it puts pressure in the tank. Usualli I just listen and watch to see when it just starts coming out the overflow, and shut water off then.
Actually, the only time I fill it that full is when washing it out, or when going to a site where there is no water. Even then, we travel with a partial tank, and fill when we get there or close. Water is heavy to haul around.