I had a quite spontaneous enema orgasm as a young man. I had re-visited an experienced nurse in south London who used to advertise "Victorian Enemas" in the broadsheet newspapers. It was my third visit to her, so we were more relaxed with each other. She was wearing her nurse's uniform, I was in her treatment room, naked and about to climb up on the couch. This time she said she wanted me, not in the usual "left-lateral" position, or else flat on my stomach, but in the "Nazi Position", meaning kneeling, bottom uppermost and head down resting on my elbows or shoulders. She had acquired a single balloon rectal catheter following a time working in the US. This she lubricated as I watched, Then donning yellow household Marigold gloves - she had run out of the thin latex ones- with a smack she separated my clenched buttocks and quickly lubricated my anus, before slowly inserting the cold latex catheter. Once it was inside, she had inflated it via a hand pump to the size of a tennis ball. This was quite erotic, and she had already enhanced the the mood by talking for some time about the uses, techniques and benefits of a good enema, as well as the various treatments requested by her clients, who were nearly all men. On my first visit I had been puzzled by her desire to chat first, as I was impatient to experience the treatment, and especially as her conversation shifted from chatting, to a monologue by her. On later visits I realized this was to get her into the mood herself, but no doubt it enhanced my feelings too. The large balloon catheter was inflated with a small black rubber inflator bulb, as used on BP machines - I think it is called an Angstrom Pump. The catheter was connected via a long red rubber tube to an enormous black rubber douche bag, hung on an IV pole, bulging with fairly hot soapy water. She ran it in fast, faster than usual, and shortly after the flow started, I had the first twinges of discomfort and began to shift my position restlessly. "That's what I like to see!" she said , pausing the flow until the cramp passed,. As she restarted the flow, she moved the rectal catheter in and out saying "I think you like this, don't you?" to which I had to agree. The experience got even more erotic when she said "I think I'll pump up the balloon a bit more!" and proceeded to inflate it with three or four more squeezes. This brought an increasingly pleasurable sensation of pressure on my prostate.
"I think I'm going to come !" I exclaimed. Just in time she placed a wad of tissues under me.
I've received many enemas from professional mistresses since then, but this was by far the best.