as always you want a fresh new biter block...... buy one here for 3.00
http://www.ebay.com/itm/ON-OFF-Switch-Bite-Valve-Tube-Nozzle-Replacement-For-Hydration-Pack-Bladder-/301769726487?hash=item4642e09a17:g:zQoAAOSwT5tWMD7k