Growing up in the fifties, once my siblings and I were preteens, our RN grandmother taught us personal hygiene and enemas became our responsibility. Shortly afterwards, my brother and I started swapping enemas with our sister, starting something that lasted until we finished High School.
A year or so later, one afternoon when my sister was giving me an enema using with a long-curved douche nozzle, it started to slip out. When I said something about it, she pushed it back in with a twist, causing me to let out a moan. That made her curious, wanting to know, what would happen if she continued to move the nozzle around without stopping. So, once the enema was in and I was holding it, she did just that. At the time, neither of us knew anything about a male prostate gland. I don't know what the douche nozzle was rubbing up against in my rectum, but whatever it was, it gave me one hell of good feeling deep inside. I couldn't stop moaning, until I explored in a large dry orgasm.
At that, my sister was even more curious than before, wanting to know what it felt like. So, she said, "Do it to me, I want to see what it feels like. When I finished relieving myself, I fixed her an enema and hung it up. While she waited in the knee chest position. After I lubricated her anus, and slowly inserted the long-curved douche nozzle, I started the flow. Once in, with warm water running, I slowly moved the nozzle around until the bag was empty. As she was holding the two-quart enema, I increased the motion of the nozzle. After a couple of minutes of moaning and wiggling around, she had really strong orgasm. After we both had really strong orgasms, the practice continued, until the end of High School.
At thirteen, I still hadn't had my first wet orgasm. But after that incident, it wasn't long, happening shortly after I turned fourteen.