I get a very hard erection when I fill myself up. If I can get all 4 quarts in me, then the erection stays. If I have to get rid of the water, the erection goes away.
A refill helps get another one, but not as hard as the first fill. Now if I get really full, am lubed up to masturbate, then the erection comes and goes somewhat. Sometimes no matter what I do, I don't get hard and come at all. It sure feels good though.
So as I get older, the coming doesn't happen as much, but I have found lately that if I have a catheter in me, I get really hard and come very quickly when I get full.
So with my meds, age, 76++ and the wife doesn't care one bit for sex, I go solo all the time. The enemas are very pleasurable, masturbation is fun and having a catheter in me is very helpful.
I don't get as hard as I used to, in my dreams I do, but reality is a different story.