Xin:i think its heavily related to this:
fantasyfeeder.com/forum/posts - these folks master a control over their throat to let air inside stomachs. there are also videos there. Go check it out
I was trying to do that, but its hard thing to do for me at least. Someone learns to do it quickly and for someone it takes a lot of time.
I've been able to do that since I was around 15, it does come in handy sometimes but if you aren't careful it can give you terrible gas. I don't know if it has much to do with the drinking thing, everything I read about that seems to involve pouring a large amount of liquid down and ignoring the choking response. That's my best guess anyway, I can't do it.