Ever notice that brass device secured to the faucet at your campsite? It is a Back-Flow Preventer. This is a required item in many states, counties and municipalities to meet health and safety codes.
What is a Back Flow Preventer?
A Back-Flow Preventer, much like a Check Valve, only only allows fluids to flow in one direction. The difference between the two is that a Back-Flow Preventer has built in vents to release the liquid under pressure once the faucet is shut off or it loses pressure. A Check Valve has no such means to release built up pressure. This makes disconnecting a hose that is under pressure difficult and potentially give you a baptism when disconnecting.