I like the stories about using pool and hottub jets, since that was always one of my favorite ways to masturbate.
The pool jet was one toy I discovered early. I first started using it when I was about 7 or 8, when I saw my older brother, who was then around 12, hunched over it, obviously intensely enjoying what he was doing. I tried it the next time I was home alone, and found out why he did it! It was great.
Our pool is shielded from the house by large bushes, so there is plenty of privacy. Except from one window in the garage. My dad had put shiny film on the window to keep the sun out, and that made it so I could look out but no one could see in. So anytime I thought someone might be doing something in the pool, like using the pool jet, I'd sneak into the garage and watch. I saw my brother using it a lot, caught my dad a couple of times, and a few times I watched my brother and his friend taking turns doing it.
One weekend when I was 12, I had several friends over for the day, and one was going to spend the night. I was obsessed with the thought of him using the pool jet, and wondered if he'd like to. While we were all playing in the pool, I went over to the jet every so often and let it caress my penis. I did it enough to be noticeable, but tried to not be too obvious about it. My friend did notice, and I saw him visit the jet a couple of times. The first time he mounted it I saw a visible look of surprise on his face. He looked around real quick to see if anyone was watching, and I pretended to be looking elsewhere. He stayed on the jet for a few seconds then left. But he went back to it several times, obviously liking the feeling.
After we had all swum ourselves out, we got out and went up to my room to play video games. My friend excused himself with some sort of excuse, but I suspected he was going back to the pool. As soon as he was gone, I slipped down to the garage to see, and sure enough, he was in the pool and mounted the jet. He stayed there awhile, then I could see him pull his suit down to get a better shot at his penis, and he hung there in concentration. Now I need to explain that this window was pretty close to the pool, so I had a very good view. I could see the concentration on his face, and after a while he stiffened and threw his head back with his mouth wide open, and I could see his whole body jerk. I was so turned on by watching this I had been rubbing my self, and came all over the wall of the garage. He drifted back off the jet and floated slowly across the pool, with his boner sticking up out of the water, and I could see white stuff still dribbling out of it. Wow.
I scooted back to my room, and he came in a few minutes later, looking a little flushed, but happy.
That night after everyone else in the family was settled for the night, I suggested we go swimming. My friend was eager. He started to retrieve his bathing suit from the bathroom where it was hanging to dry, but I stopped him, saying we could go skinny dipping. He said 'cool,' and we quietly went out.
We swam around for a while, then I decided to make a move by going over to the pool jet. I hung in front of it for about 30 seconds, which got me hard, and then swam off. He hesitated a little, then did the same. So we alternated, and eventually we both got our rocks off on the jet, standing close to each other to watch. It was one of the most exciting times I'd ever had, and when we talked about it later, he agreed he'd really liked it, too.
We did that together a lot after that first time.