Enemas were always a tough topic for me to bring up when I was dating. I was not very outgoing when it came to the ladies, so most of the women I dated ended up being closely connected to friends or relatives, and I was mortified that my dirty little secret would become semi-public knowledge.
This was not a carefully devised plan, but for some reason I was a little more comfortable aaking them if I could give them a douche or watch them. That seemed to me a little more like a harmless (if just a little twisted) voyeuristic fantasy - nothing to do with butts or poop. I crossed that bridge with, I believe, 5 or so of the women I dated, 2 of whom were willing to go there (though neither routinely douched before or after).
With both of those who agreed to let me douche them, enemas eventually entered the picture as well. With the first, who was probably the least inhibited woman I ever dated, it was relatively easy to bring up. In fact, I just went there right away after I got a “sure, we can try that” response when I asked about douching, and got a “eh, why not?” i would not say she ever really got completely into enemas, but she always masturbated and came hard when I gave her one.
One time when she was really constipated but was mad at me for some reason ("C'mon. What's wrong?"; “I SAID NOTHING!!!!”), she left an enema bag hanging to dry in the shower and a vibrator on the vanity for me to find when I got home from work. Normally that would have really turned me on (and on some level, of course, it did), but I knew it was also meant as a super passive aggressive “fuck you”. She had shut down all enema activity for many, many months prior to that - even the night before that incident when she was painfully constipated - along with just about any other form of sexual interaction. Hard to believe that relationship didn't work out, huh?
But I digress. The other lady who let me douche her is now my wife. While she is not naturally super adventurous sexually, we have a great relationship and she is willing to get out of her comfort zone a little bit to make me happy. And in turn I accept there are some things I long to do that will rarely if ever be on the table. She let me give her an enema for constipation a couple of times but absolutely hated them. She also took no pleasure when I douched her and is concerned about ill health effects, so that has only happened a few times - the last of which was many years ago.
On the other hand, she happily gives me an enema and blowjob weekly, and we have great sex otherwise several times per month (which ain't bad for people married ~20 years and in their 50's).