I don't know if this is appropriate to say but my youngest son likes using our vacuum cleaner from time to time. I have walked in on him a few times. The first time I saw him doing it I was quite upset and thought he was hurting himself.but then he explained to me that he doesn't let the vacuum suck his penis into the pipe. He just holds the vacuum pipe close to the tip of his penis and then the air that rushes past, makes his foreskin flap. He says that the flapping brings him to a very quick orgasm. He got the idea from the swimming pool water jet. That is most probably his favorite way of masturbating. He says it does the same thing. In both cases his foreskin flaps really fast, resulting in a very quick orgasm. He has never complained about pain or anything, so I don't think it is doing him any harm.
I use a 2 inch silicone radiator hose hooked up to my shop vac, a little vasoline and I'm in heaven, been doing it more than 20 years, sometimes 3 times a day