The B-108288-4PK Duckbill Valve, is designed to replace your existing Flushmate duckbill for your Flushmate system. The duckbill valve is located under the cap on the Upper Supply Assembly. The Upper Supply assembly is located on the top of your Flushmate system and has a hose connected to it from the water supply. The Duckbill Valve open and closes to add air to your Flushmate system during the recharge process.