There was a thread a while back about the extra work involved in preparing for anal intercourse. I think it had to do with the justification for an upcharge for that particular pleasure. (Which is fine btw, it's not what I'm interested it.)
I remembered thinking at the time. "Is it really necessary to have a couple of enemas beforehand?"
I'm bringing it up now because this morning I enjoyed lower congress with a lady who I know wasn't (necessarily) expecting it and (I'm quite sure, though we didn't discuss it) didn't do anything extraordinary in preparation, beyond her usual perfect hygiene.
Folks, we did multiple penetrations from multiple positions with some really deep penetration. There was never the slightest unpleasantness. This was not the first time but it has always been the same in that regard.
I attribute it to a good diet with plenty of fiber and lots of water. I just don't think a healthy digestive system leaves much in the rectum.