Catheter play sounds like a fantasy of mine. All done with unused sterile supplies. The supplies can be purchased either on line or in any medical supply house. I was taught by a nurse several years ago how to do it and if done carefully there is no danger.
I recently had to have a stint removed from surgery thru my urethra and you can believe me when I say that is nothing to play with if you aren't a dr, could probably easily damage yourself. Plus I didn't find it to be enjoyable at all.
Medical play is another complete thing then what goes on in a hospital. Inserting a catheter is painless the only discomfort is after removal. The first time you void your bladder there is a little sting. Purchase a Foley Catheterization Tray for less that $15. It has every thing needed including gloves The Foley catheter has a balloon at the end of it that is filled with sterile water to fix it in place. It can't be removed until the water is removed. The denial of bladder relief is a masters control of the slave. They come in several types male and female. The diameter of the tube is also a selection.
I used to try this on myself when I was only slightly younger. Any guy thats going to try it, don't do it when your rock hard, try it when your like semi-hard and getting worked up. If you do it when your hard, its going to hurt more and more.
I should say, I stopped right after I had a surgery because after the surgery I had to wear a catheter and wearing one of those things felt so uncomfortable. Because of that, the thought of even doing this kind of play makes me squirm and I haven't done it ever since.