Right, the reason frost-proof faucets work is because there's no water in them when not in use. The valve is at the far end, 12+ inches into the house (the wat

Right, the reason frost-proof faucets work is because there's no water in them when not in use. The valve is at the far end, 12+ inches into the house (the water on the other side of the valve is never cold enough to freeze). And the pipe is angled ever so slightly downward, so gravity ensures that any water left after closing the valve flows out. That's why you can't leave a hose connected - it leaves open the possibility of preventing water from draining out before it freezes.