This question has to do with a (party) function of this equipment. I haven't used one so I have no clue.

A friend of mine is hosting a lobster party. She was looking for something she could walk around with on her back to dispense refreshments on-the-spot. Is the camelback a bite valve and suck or is there enough pressure on it's own if you press the valve? I imagine it is the former or there may be a lot of choking athletes out there.