As I noted in my original post in this thread, medics have most often been unsupportive of the use of enemas to relieve constipation. The latest NICE guidance shows a change:

"The case for adopting Peristeen for transanal irrigation in people with bowel dysfunction is supported by the evidence. Peristeen can reduce the severity of constipation and incontinence, improve quality of life and promote dignity and independence."

NICE is the "National Institute for Health and Care Excellence"

Peristeen is a pump driven enema system. I don't see that it would give me any advantage over the gravity fed DIY system that I described in my original post. My system is, moreover, far less expensive.

Although the NICE guidance is for Peristeen explicitly, I think that the guidance will apply to water enemas in general.

("Transanal irrigation" is being used as a synonym for "enema".)

Reference:

[1] NICE Guidance
Peristeen transanal irrigation system for managing bowel dysfunction
Medical technologies guidance [MTG36] Published date: February 2018
Peristeen transanal irrigation system for managing bowel dysfunction | Guidance and guidelines | NICE

John