Yes definitely. To begin with, having anal with a dirty anus is just not right as it can smell and turn ur partner off. So it should definitely be cleaned as it is easier to have anal as the stuff in won’t cause as much friction and it’ll be more pleasurable for both you and your partner. As for STD, you don’t get STD because of poop. STD is a different disease that is transferred if the other person has it, poop won’t affect its chances