Reservoir can removed and filled while leaving the hose threaded through the pack and turned inside-out for easy cleaning. The opening automatically shuts off when the hose is removed. Smooth inside, for easier cleaning and slightly smoother outside, to slip in and out of packs. BPA Free. Top closure is fold-over and slide-closed eliminating leaking and opening fully for cleaning. Utilizes the Hypervalve Hose which incorporates an on/off bite valve.