(sorry if disgusting question) why do slash fic writers rarely mention anything about intestinal cleaning before butt lovemaking happens? was there a tacit fandom agreement to imply but never say? do fics happen in the "everything is the same, except everyone's rectum always ready" AU? nothing dims my ardent love for Large Amounts of diverse-in-positions-and-dynamics erur smuts; am surprised, of hundreds fics i read, maybe one or two mentioned, in a few words, prep taking place???
So there are two answers to this question…The first is that fanfiction is fiction and the main purpose of fiction is not to provide an accurate representation of the world. The main purpose of fiction is to entertain, to move you, to make you think, to turn you on, to make you feel myriad other emotions. Accurate depictions of reality are not a necessity to do any of those things. In fact I’d argue that when it comes to smut, too much realism can get pretty dull pretty quickly. I’d rather read (and write) sex scenes that focus on emotional intensity rather than the mechanics of inserting tab x in slot y. Having said that, everyone has their preferences, and some people do get off on the prep side of anal sex, in which case go for it!
The second answer is that, in real life, not everyone bothers with the specific kind of prep you’re referring to. Some people do, some people don’t, it’s a matter of personal choice rather than the rule of law. It’s ironic that there seems to be a bit of an assumption among some readers that prep absolutely has to happen every single time, even though it’s rarely written explicitly into sex scenes.
One fic I can recommend that does explicitly mention prep, is all your demons and desires and dark sides by brightly burning. Be warned though, in this case the necessity for prep is related to trauma and ptsd, however it’s very sensitively handled.