I was in an unusual situation with this because to went through about three years where a very attractive married woman gave me a calculated series of "correction enemas" after catching me giving myself an enema with her douche nozzle.
Every three of four weeks she would sternly arrange an over-the-knee enema series, my erection between her stocking thighs. She insisted I witness an elaborate process -- totally nude -- beforehand of her shaving an Ivory soap bar into a large jar, adding hot water, and then shaking to agitate the solution, while I would stand with a stiff erection -- my hands ordered behind my back -- watching her mix my soapy enema before a cleansing enema. She would use a large curved nozzle ... much larger and thicker than normal ... and knew exactly what she was doing as she used the bulbous, fluted tip to vigorously massage my prostate during the enema process.
She would go into detail with her lecture during the preparation and the administration of the contents, and make comments about my erection and the precum at its tip. "You hold your enema! Take your enema and quit twisting. Hold your enema!" She would give about a 2 1/2 quart ivory-soap enema and then a 3 quart cleanse. She delighted at my gasping, always urging me to "just a little more." She would stop the flow, massage my abdomen and whisper "Listen" every time she would release the clamp. I bet she did it ten times ... knowing I needed release too. She was obviously turned on by it ... although we never touched one another sexually except for her probing finger that would stay in my bottom for several long minutes at a time..
Instead, after I was full of my soapy, she would demand I produce "proof" of how sorry I was I used her enema. So I would get a soapy fistful of water and jack off as I was ordered to "hold" my enema all the while. Several times she ordered me to ask for permission to come but that never happened. Only after proof -- my ejaculate -- could I expel the first enema, wait the 15 minutes for the relentless lubrication finger, and go back over her knees take the cleanse. She was very insistent the cleanse be complete and insisted on the extra volume before she withdrew the nozzle.
At first she would do this 45 minute ordeal in private ... this was in the early 60s ... but soon two or three of her 40ish year old female friends were invited and loved to watch our enema session. I never had sex with any of them and while several felt the firmness of my penis and another enjoyed the finger probe, my masturbation was totally my own. They would watch in the bedroom, usually with a glass of wine, and allow me to expel in private. In later years one confided it was the most erotic scene they ever seen and admitted to enemas where they would 'jill' afterwards.