I would always take a dump in the morning but if I had to take a second dump I knew I was going to win that day.
Dump in the morning, pee right before the race. Gotta shed weight in any way I can. I also sit on my bike in pregrid and run laps in my head. Think about my brake markers, where I will shift up and down, run my lines. I even practice my starts in my head. Then when I hit the track it almost feels like auto pilot.