I was recently honored with an email from a wonderful gentleman who has a very good disciplice on how to prepare for strap-on play...he was taught very well by a wonderful Mistress...
here is a good procedure to follow...
Actually I start preparing for the session several days in advance
Since, I know they are just as important for your pleasure as the
pleasure I derive by pleasing you. First I abstain from having any
ejaculations from three to (even as much as) seven days before the
session. Second, about twelve hours prior to the session; do not eat
any solid food. Then in the morning of the session; an enema to clean
me from inside as nothing could be off limits during our play. Lastly,
I also shave my butt and genitals. This way anywhere you touch me I am
totally clean.