Mueller 104-513 Anti-Siphon Frost Proof Sillcock 6""Mueller" Frost Proof Sillcock Anti Siphon Frost Proof Wall Hydrant : Prevents outside faucet freezing and protects against back siphoning. A built in backflow preventer checks siphoning back into the water supply. The sill cock drains automatically upon water shut off if the hose is removed or open. 1 2" nominal copper sweat or 1 2" M. I. P. Highlights: 6" length 3 4" MHT outlet 1 2" MIP and 1 2" solder input Anti siphon protects against back