How Tour de France riders relieve themselves

In the first five to ten minutes of a race, riders pull to the side of the road, pull their shorts down just like you would underwear and do their business. During this neutral rollout, there's lots of time to catch back on to the peloton.

Once the pace picks up, it's easier to wait for a lull in the race when a big part of the peloton pulls to the side of the road. But, they also pee off the bike while riding.