AMERICAN STANDARD 1660400.002, 1/2-Inch NPT In-Line Vacuum Breaker in Chrome

To prevent water from a handheld personal shower from flowing back into the clean water supply, simply install an in-line vacuum breaker between your wall supply and flexible shower hose. Installs between any wall supply and flexible hose on hand-held shower. Prevents back flow of water into supply piping (May be required by code in some states).