Anal sex?

So, I'm a little curious about how anal works. I understand that you put the dick in the asshole, that's pretty obvious. But it's my understanding that you want to avoid the dick touching any poo for obvious reasons. However I'm curious about how you avoid this. Do you guys take laxatives if you know you are having sex that night? Do you have to wash it out to make sure there is nothing on the walls of the rectum? Just some basic questions about the preparation for anal.Thanks guys!