Kent- If it's any help, tell your son to try a bladder full of water with some lemon juice added. ( I would let it sit for 24 hours ) Maybe that will help. As I said, mine is milspec surplus and not a "camelbak" branded one.
Tom, I read the "rule" somewhere and a newb needs ten posts before posting pictures. I am there now and although the pics aren't that exciting, I'll try and post them later today.