I remember enemas I got as a child, from parents or my aunt. Embarrassing, painful, and horrible. When my lover wanted anal sex, I could not imagine doing it in bed without first cleaning myself out, so I did a few discreet small volume enemas before he arrived. Mixed success, I wasn't happy to have to clean up messy sheets, even though we used towels, etc.
I had a 2 qt douche/enema combo syringe with the usual nozzles. So he took it upon himself to buy two more large bags, connected the hoses together with a T connector from the hardware store, and a new clear hose coming off the T.
He found a large dildo, with a hole down the center, looks just like a urethral opening, with a cheap squeeze bulb attached to it. I think it was supposed to squirt something to mimic a guy coming. Yeah, like that worked. He was able to push the clear tube down the center of the dildo to turn it into a nozzle. The tip is pretty bulbous, I couldn't get it in for a while.
We always do enemas in the bathtub because we know that no one's control is perfect, and clean up is easier there.
So he starts me out with one bag of hot water, smaller nozzle and lots of soap, and I have to hold it in while he rubs my pussy, but never to orgasm. Over a period of hours he repeats that until he thinks there is enough room to start the larger enemas, and I am not allowed to come. Usually he likes me to do a minimum of four soap enemas before we begin.
If it has been a while since I was penetrated anally, either by dildo or his cock, he gives me another enema of plain water, and while I let it out in the tub, he takes a soaped up hand and pushes his fingers in my ass one at a time until the water stops flowing out. Of course, I try to push his fingers out, and they just slip deeper. This makes it easier to take the dildo nozzle, but it always hurts as it goes in.
After I take both bags, my lover uses a Doc Johnson penis shaped large butt plug in my ass, it goes really deep inside me, and he kisses me for a long time. He gets really excited when I beg to get up. If the pain gets really intense, he puts nipple clamps on me and makes them really tight. He always knows when he as them tight enough because I am no longer concerned with the enema cramps, all I can feel is my painful nipples.
We do this several times until he is satisfied I am all cleaned out, and take a break, since I am a wreck from not coming all those hours. This also lets my anus contract again from all the stretching so when he pushes his cock in it's tighter and better for him. When we do make love later, I can climax as many as twelve times. If my anus is still stretched out, he puts a really big dildo in my pussy, which makes my rectum much tighter. I hold the dildo in with one hand, and rub the attached balls on my clit while he takes his time in my ass.
I think the only way to improve our enema routine would be if we had a double balloon retention nozzle, and some way to install restraints in the bathroom. My lover wants to train me to accept his choice of enema no matter how hard it is to take. If you remove the option to stop, all you can do is take it.