The reservoir can be removed and filled while leaving the hose threaded through the pack. Reservoir can be turned inside-out for easy cleaning. The opening automatically shuts off when the hose is removed. Smooth inside, for easier cleaning. Slightly smoother outside, to slip in and out of packs. BPA Free. Top closure is fold-over and slide-closed resulting in never leaking and opens fully for cleaning. Utilizes a hose which incorporates an on/off bite valve.