*sarcasm* Oooooh... the sexy part of anal sex.
Well, let's face it, it is not possible to keep it clean all the time for spontaneous random occasions. Any guy that tops you should expect that shit happens, especially if it is spontaneous and random.
If you are planning a night with anal sex, then you should wash out with a douche or enema. My husband has a fleet enema bottle he keeps for travel and we've installed a shower attachment for home use.
As for how to do it... he fills the enema with warm water. Lubes his sphincter and inserts the nozzle inside. He then squeezes the bottle, removes the nozzles and releases his bowels and flushes himself out. He repeats that until the water comes out clear.
After that, he then starts teasing me and starts getting romantic/sexy. That way, the romance and sex aren't interrupted while he preps.