Deuter Streamer Tube & Helix Valve mouthpiece is leak-free thanks to its water-stop locking action. Simply turn to open. Light pressure activates the drink opening, which provides a pleasingly high flow of liquid regardless of the position in the mouth. When done drinking, the integral spring valve automatically closes the mouthpiece. The “Hi-Flow Bite Valve” is easily disassembled for cleaning. The attachable protective cap keeps the mouthpiece free from dirt during longer journeys.