Before you go anywhere near there you have to make sure it's clean, shower together if you can so you can see it cleaned to your satisfaction and then before doing the deed spread those cheeks and blow gently on the hole.
If you get a whiff of anything back, go back to step 1 or change your plans.
You can't play around with human waste, keep it clean.
Also? Use a dental dam. Some people say it ruins intimacy or is too fiddly but it's worth the reduction in risk IMO.