[HayZee518]

an anti siphon valve has an air gap engineered into it. when there is normal flow, the water bypasses this air gap but when you shut off the hose the air gap is open preventing a back flow into the water system. the frostproof faucet is called a "hydrant" it looks like a regular faucet and the way to tell if it is a hydrant is to look in the basement at its connection. the valve body is about a foot inside the house. soldered to the cold water tubing. inside the body is a long tube that houses the "stem" part. outside there is a gland packing which orevents water from coming out the stem and spraying everybody in sight. its basically the same in theory as a regular fire hydrant. the valve part is at the bottom of the stand pipe located way down in the earth where the hydrant taps into the town water supply. water comes up in the standpipe and out the spigot - the part with those caps on it.