Unless it has a ‘poopy butt’ – just clean the butt! But generally rabbits cannot have their whole bodies wet as it can put them into fatal shock! The reason is because water that soaked through rabbit’s fur can cause a sudden change in temperature which is traumatic and could cause the shock.
Bunnies are very clean and groom themselves all the time!
References
https://rabbit.org/the-dangers-of-giving-a-rabbit-a-bath/
Better Life for Bunnies 