We just took one of our existing Camelback backpacks and wrapped it around the roll cage behind the seat. A pair of bladders and drink tubes was switched out at each pit stop. It was always one person's job to switch out the drink. Most of our drivers are disease free, so we weren't too worried about germs and grossness.
Two tips:
1. Always be drinking during yellow flags. Or, if you have the misfortune, red flags. The Camelback bladder should be near empty by the time you pull off. If it isn't, you aren't drinking enough or you flipped your car early in your stint.
2. Find someplace easily accessible to put the water line. You can't move around a lot in a 5-point harness and searching frantically for the straw is a real pain.
-Kyle
Eyesore Racing
"That's probably wrong, but it's worth a shot."