My "new" 45 has a fresh water flush vacuflush toilet. The fresh water is always under pressure. As soon as you flush, water is provided. There is a shutoff ball valve at the head to simplify servicing. Very simple system. Water cannot backflow, as its always pressurized. Even if the pump is turned off, there is no way water would be able to drain back to the supply tank, as there is a mechanical valve at the entrance to the head. I don't see a need for a solenoid. I love it. No more smell or complicate winterizing.