Groco HVL Bronze Vented Loop for Hose Connections The Groco HVL Vented Loop allows air to enter to break siphon, but does not permit air and odors to escape. This series of vented loops assures clog-free, anti-siphon protection for sanitation or engine exhaust systems. The oversized vent valve can easily be removed for inspection or cleaning without tools. The cap is threaded 12 NPT to accept a barb fitting if you wish to vent overboard. Overboard venting is required if this HVL loop is used in