She has had her thorough enema, say around 11 pm, cleaned out well but not allowed to orgasm; then about an hour later, 6-8 oz of very warm mineral-oil into the rectum prior to anal sex that takes her to orgasm.
She is tenderly wakened about 4 am and helped / turned over on her tummy, so that she is spread-eagle on the bed, legs wide apart. The tip of my index finger is very carefully positioned so that it is against the seal of her anal ring; and kept there for a few minutes while she adjusts to it and awaits insertion.
The anal seal is tested and tested until, finally, about one inch of finger is ever so slowly inserted into the anus. The finger is kept there while she continues to adjust to it.
When she is ready, the remaining full length of the finger is very slowly inserted all the way up into the anus and rectum, so that she takes the entire length of the finger. In this penetration, she is given slight twitches of the finger in her rectum, so that she is able to "answer" the slightest movement of the finger with a clenching of her inner anal muscles. Thus begins the long "conversation" between the finger and the anus, gradually bringing her to intense rectal and anal arousal as the twitch-clench "conversation" goes on and on and develops into a profound anal and rectal relationship that can only be appreciated if a man and a woman experience it themselves.
Anal and rectal and intestinal tubes and enema devices can be added to this, along with urethral catheters; however, there is nothing that can substitute for the relationship between the inquisitive finger, fully inserted up into the inner anus and rectum, giving the exquisite twitches and testings to her anus and rectum, causing her to answer those exquisite "signals" with her anal clenches and rotations on and around his wonderfully deep, inquisitive finger.