I've never really done much prep work for butt play. Maybe do a quick wipe-down with a wet wipe (which are good to have on-hand for clean-up afterwards, too), but that's as involved as it gets. Then just grab the lube and I'm good to go! Obviously if I'm having actual anal sex, some prep work with fingers and/or smaller toys first is necessary to make everything comfortable and pleasurable, but I don't really do anything special to prepare for starting to put things up my bum.
Obviously if I feel like my digestive tract is backed up, then it's not a good time for butt play, but I have a reasonably good diet (mostly, anyway), so that's not usually much of an issue for me.
Honestly, I've never quite understood why some people do so much elaborate prep work before anal play. Everything I know and have read about the workings of the human body says that stuff isn't necessary, and can potentially even be harmful (either outright harmful to your health, or harmful in the sense of being self-defeating and creating weird, unpleasant smells and the like), so why bother? I guess if it makes a person feel more comfortable and less self-conscious, then it serves a valid purpose, so to each their own (so long as they're not doing anything that potentially endangers their health), but I still don't really get it.