JB-here's more on your question:
Glycerine IS the active ingredient. It is extremely hygroscopic and promotes evacuation by being an irritant to cause cramps of varying degrees, as well as by drawing water into the colon. So, if you want something that is very hard to hold, use straight glycerine, up to say, 8 ounces, maybe a pint. If you want something to really clean you out, use 2-3 quarts water with about a pint of glycerine. You will have a few good return trips to the toilet after the enema is completely expelled because the residual glycerine continues to draw water into the colon, not because you didn't fully empty.
If you want your enema over and done with when you finish expelling, DO NOT use glycerine or epsom salts. Plain water is great. You can even do two or three enemas in a short time if you just get it in and get it out. If I want a quick enema in the morning because I have something planned for that evening, I can do 2-3 quarts in 10 minutes from the time I decide to do it until I put the equipment away after my shower. Later in the day, maybe before my girls come home from school, another ten minute, 2-3 quart quick enema, will have me very clean and with absolutely no residual water or "brown tinted mucus" for my husband by the time we go to bed.
A lot of people talk about wanting a very thorough cleaning. WHY? It won't promote any better health or evacuation later, and unless you are having a colonoscopy or are having very prolonged anal/rectal/colon sessions with long repeated deep tube or toy insertions, where you feel you have to be spotless for your partner, you don't need that.