Huz had one last year. He had to drink a half gallon of Gatoraid along with the 8 ounce bottle of prep fluid. I suggest you make sure it's cold/well chilled or you may throw it up, he did.
As for sore bum....get some of those wipes. A name brand is Tucks, but we got the generic that worked just as well. They come as toweletts or round pads in a jar.
As others said....the prep is the worst part.