Apollo™ Air Gap Drains (AGD4Ax) are designed to funnel minor discharges from a Reduced Pressure Backflow Preventer's relief valve due to line pressure fluctuations and/or minor check valve fouling into the drainage system. Drainage piping is easily attached to the threaded portion of the AGD. The female NPT size is listed in the table under Outlet Connection. Drainage piping may be attached with a coupling and the appropriate cement or with a flexible pipe coupling. Piping compatiblewith the outlet is listed in the table under Outlet Pipe Size.