Some doctors give you the drink
to drink at home and then you go
to the lab
to get your blood drawn an hour after drinking it. I think the main practice now is to have you drink it at the lab, sit there for an hour, then get blood drawn (that's what I did the last few times I've had this test done). I was allowed to drink water while there, too. You have to chug it, though, so I don't know if they'd let you use a straw.
Laura- yeah, it's no biggee at all!