some BLs do show(the act not the shits) or at least mention the bottom doing their cleaning prep. but then again you shouldn't expect something realistic in a FICTION especially about the poopy farts. imo the point of fictional smut in general is so we don't have to experience the tiring and awkward side of the sexing (unless it really serves as a plot point or sumthing)
So I'm a bi man myself and even though I'm trans, I'm a top. I've fucked cis gay bottoms before. They usually prepare before and actually clean it inside. With sex you should be showering before AND after, being clean is very important. And when you are starting your foreplay, lube is very very important. The asshole is very tight and 2 fingers usually isn't gonna do it- but a lot of bottoms also prepare themselves for that. Its not the greatest comparison but there are a lot of pornstars (mainly woman) who do like stretch training for their vagina so they can take those really huge dildos, some bottoms do similar to that but with smaller toys or fingers. Also, I don't think a lot of people really wanna read realistic sex and I'm definitely one of them. There isn't really a problem if people don't wanna read realistic sex, at the end of the day its just a yaoi story and not supposed to be based on real life gay relationships.
Don't worry it's not rude at all! I'm female to male, so I was born a woman but transitioned into a man. I only have top surgery and haven't bothered with bottom surgery because it's really expensive and at the moment I can't afford that, I probably won't ever actually bother with it. I do take testosterone injections and if I'm going to have sex, I use a strap-on. I do pass as a man though, the only thing I haven't done is just bottom surgery.

How do gay man shove dick in their unprepared asshole? Isn't it unrealistic how shit doesn't come out? I literally bleed if my shit is a bit fat