I posted a reply a while back, but to recap, although the valves are probably glued in the can be removed for cleaning, or replacing, the knack to replacing them is to use a small piece thin of string. Attach the string to the inside bit that goes inside the tube and pop it into the tude. thread the outer piece on the string. The string now allows you to pull the inside bit into the hole and hold it whilst you screw the outside bit on. Glue them in if you like but they can work without glue. Evo stick saves messing around with two part glues, just make sure its very thinly applied, ie use a samll paint brush.
Paul Lemmer used to sell this tip for the price of a round of drinks. To you its free, because one day I will need something from the members of this quite brilliant and informative forum.