I was about 23 or so when I found an enema bag at my grandmother's house. it was a plastic one with a ziplock opening at the top; I hung it up in the shower and filled it while I was showering. Using a bag, it was a wild way to get an erection and keep pressure on the prostate while I masturbated.
That was 22 years ago. I was a plumber in an earlier life, and eventually got tired of the bag, so now I have a permanent full-pressure system.
now, I know what I'm about to say, some people are going to scream and claim I'm nuts.
I live alone, no risk of anyone who doesn't already know walking in.
I created my own hose to attach to replace the exiting shower head. In the wall where all the piping is, I have access to it through a closet. I took the elbow off that normally goes to the shower head and replaced it with a T. About a foot above that I put an elbow into the shower. So there's one elbow that has the angled arm for the normal shower at about 6' 6" height, then at about 8'6 is another straight nipple coming through the wall with a 3/8 shutoff valve like you would see under the sink. The 3/8" hose fits on the end of that with a compression fitting, like the kind used for refrigerator ice-maker water supply.
That hose is about 10 feet long. About 2 feet from the loose end, I put a 3/8 ball valve, so there is about 18 inches of hose past. I sanded the "nozzle" end of the hose to make it smooth for insertion. The ball valve has a handle that's about 1 1/2 inches long, so I can modulate the water pressure while recumbent or squatting.
So for all the people screaming that normal household pressure is 50 PSI and can easily cause a ruptured colon, you're right. But with the ball valve there, the pressure is as little or as much as you want it to be. I noticed over time that I could (did) increase the water pressure as my abdominal wall muscles got stronger. I'm pretty sure now that the pressure I use is far greater than what caused discomfort when I started.
Yes, there is always a risk of using too much pressure. So far (14 years of this system) I have not had any problems. I guess it's just paying attention.
When the sphincter is relaxed, using full pressure doesn't cause a problem because what goes in goes right back out, it never gets any deeper than the rectum, and so "it's a wash". That's more of a douche concept.
I created a "portable" system, where i can just screw the existing shower head off and put my Y-connection in place with it's own shower head on one branch and the nozzle on the other branch. Bring some soft-jaw channel-lock pliers just in case the existing shower head was muscled on.
I did get into trouble the first year I did this by getting too frequent; I wiped out my potassium and that was an eye-opener. My legs and major muscle groups felt like they'd been beaten with hammers. I'm on a diet of basically fruits and salads now and haven't had that problem in ten years or more.
I feel great, I've lost about 60 pounds since the time I started, and I haven't had abdominal cramps (except when away from this system) since 1998.