Mel wrote a review of CamelBak Big Bite Valve Mouthpiece on April 6, 2013
Just got a Camelbak Groove water bottle and the bite valve seemed to be completely sealed shut with no opening. Tired to bite on it, and suck out the water like you're supposed to do, but nothing...slit it open with a knife, but that was a very bad idea because it caused the bite valve to leak water when turned upside down. Returned the whole bottle, and got a new one. Same problem! This time, however, I took the bite valve completely off, and soaked it in a glass of very hot tap water (not boiling, just hot from tap) for about 20 seconds. Then I squeezed it together, and voila, the bite value opened right up! Now I love my new Camelback Groove water bottle--delicious, filtered water!