I’ve never sucked a cock that has been in my ass, but I have rimmed a few guys on occasion. It has usually been after we’ve showered and I’ve actually washed his ass myself, sliding a finger in a bit to tease him, but also to try and clean it thoroughly.
Now I’ve had my ass eaten plenty of times, especially by one friend who doesn’t care how clean I am. He will lick and suck and poke his tongue in and out. He will lick his finger and stick it in, rubbing my prostate, then pull it out, lick it, and slide it in again. I always clean myself out before hanging out with him, but I haven’t “sanitized” myself back there.