When I fill the fresh water tank to the point it overfills ours, too, will continue to siphon for several gallons. I found that to get the siphoning stopped, just turn on the faucet at the water bay for a few seconds. First stop the water going into the tank by closing the water fill switch, then turn on the coach's water pump, and finally turn on the water bay's faucet. I assume the act of pulling water out of the water tank stops the siphoning due to the need for air going into the tank through the overflow to replace the water which the pump is pumping out. I also suspect that "over filling" the water tank makes its sides bulge out a bit, and that would add pressure to the siphoning effect making siphoning a bit more difficult to stop.