vers_sil,
1. Get the "Big 4" tested & if necessary, taken care of. (gono, syph, chlam, hiv)
2. Consulting with your doctor, get all the "gay vaccinations" (hep A, hep B, mening ACWY, mening B, HPV).
3. Get on PrEP. (less chance of getting HIV)
4. Morning of - and, if it makes sense to your medical situation: take a doxycycline. (less chance of getting chlam & syph)
5. An hour or two before going: clean out your poop chute...enemas until you're expelling clear water.
6. Really just before going: probe up there with a dildo, both to loosen & lube your hole, and to coax any secretly-remaining enema water to expel.
7. Dress in shorts that you can easily kick off when needed.
8. Have fun.
9. Enjoy knowing that other guys' cum is inside you and absorbing into you.
10. Figure that you could have picked something up and had better lay low a few weeks until you can re-test.
11. Re-test everything (repeat point number 1!!)
12. Figure "you had your fun" and should maybe get back to being a humane, sedate type of person.