Surplus 3L bladder - army surplus - camelbak Specific style and availability vary, Used, recommend sanitation prior to Use large Neck style, comes with hose and Big bite valve Air pressure Leak tested. The grey buttons at the Big Bite Valve and the connection to the Bladder Stem are to disconnect the Valve from the Hose and the Hose from the Bladder, for Cleaning repair replacement or Connecting to a Gas Mask Adapter