The race car drivers don't go to the bathroom while racing. You go before you get in, you go after. Even though they use a hydration system and sometimes grab a quick water bottle on a pit stop, they sweat enough to help relieve some of the need to go to the bathroom. The hydration system replaces what they sweat out and they can lose up to 10-15 pounds per race, depending on the heat and the length. The race is only a few hours long so hopefully they can hold it.