Just to echo the views above - the preparation spoils the spontaneity. When I want anal sex, it's usually in the heat of the moment - I just want to do it, there and then. If you plan for it, when the moment comes, the impact is lost.
If you're *really* squeamish about poo, then maybe anal sex isn't really for you. It can be icky and smelly sometimes, but then so can all good sex.
That said, I've had anal sex, oh, I don't know, hundreds of times probably, and only twice I have had an accident. Sometimes when I'm doing it I get the feeling I really need to poo - and almost always I can control and ride that feeling. A couple of times I got that wrong, with rather embarrassing consequences, but I must stress that is very rare.
Usually all you need to do is have a good wash around there, but I obviously need the loo, I do my business and then have a wash and wait for a bit. My partner is a bit more fastidious - she insists that she always has a poo before we get down to it, just to be on the safe side! Which I have to say, rather takes the romance out of proceedings...