Prier Products Diamond 8-in L x 1/2-in Mip Brass Anti-siphon Half Turn Sillcock in the Sillcocks & Hose Bibbs department at Lowes.com
Woodford Model 17 4-in L x 1/2-in Copper Sweat Brass Anti-siphon Push/Pull Sillcock in the Sillcocks & Hose Bibbs department at Lowes.com
Eliminate/Fix Your Hose Bib Anti-Siphon Valve or Vacuum Breaker Spigot Once & for All ~SpigotMaster - YouTube
Everflow 62061P-NL Anti-Siphon Sillcock Frost Free Outdoor Faucet with 1/2 in. PEX Connection and 3/4 in. Hose Bib, 6 in. Long : Amazon.co.uk: DIY & Tools