Eh, the mouth is the fount of vomit, but I bet you don’t mind kissing it. If you clean down there, you shouldn’t be encountering shit during the act. As a fellow ‘not anal lover,’ I can assure you, it still feels good to the other party. Use a dental dam, douche before sex, and encourage them to use a butt plug during vaginal sex (because both being filled is so much better).