If I am hooking up with a guy, I would expect him to be prepared. That means "pristine" clean, outside and inside. Yes, there may still end up being some minor traces; I'm a big boy, I know how bodies work, and if I were that squeamish, I wouldn't be playing around with buttholes, much less sticking my dick in them,
On the other hand, I have been with a couple of guys who didn't think twice about offering up their holes, knowing full well that they were not in the least prepared. and when I expressed dismay, they couldn't understand why I was being so demanding. NOT. OK. NOT. It's revolting, incredibly indelible (I'm glad it was their bed, not mine), reeks, and is not at all what backdoor lovin' should be.
Most bottoms, god love 'em, are more self-respecting than that, however, and are in-tune with their bodies and how they need to prepare. When done right - man, there's nothing like it!