This was posted on Zity in the category discussions/pooping and messing/solution for an uncontrollable urge; I copied and pasted the whole thing below. I have tried this; it is a no-doubter, and does not result in a lot of liquid. The glycerine is the active ingredient; the metamucil just adds bulk and fullness. It is important to keep it cold so the metamucil doesn't swell; I used a little less poeder, and slightly more water just so it was thin enough to flow through the bulb syringe. Knee--chest works well to make sure it flows into the colon. It doesn't take long, and once you get it inside you, there is absolutely no going back - just going.
The following was copied from dailydiapers.com, enjoy:
believe I've finally lit upon the perfect enema mix. What I've been looking for is:
Small volume needed
Creates a big volume of poop
Poop is very soft and squishy
Urge to poop is unpredictable
Urge to poop is impossible to resist
Easy and innexpensive to make
Here's my recipe:
In an 8 ounce container with a screw-on lid mix 4 ounces of glycerine ($3 at WalMart) with 1 ounce of cool tap water. Shake well. Add 5 tablespoons of Metamucil (or equivalent...$6 at WalMart). Shake well until dissolved. If no Metamucil is visible, add a little more. Keep adding until it won't dissolve. Note: do NOT use warm or hot water for this! The cold water will dissolve the Metamucil but it won't start swelling.
Put the bottle away for 24 hours to let the Metamucil fully dissolve.
Prepare your diaper as you wish.
Shake the bottle of liquid to re-mix everything. If it looks as thick as honey, add a LITTLE bit of water so its about the consistency of syrup. You need it to be a little runny so that it will come out of the enema bulb and will be able to work its ways into the nooks and crannies of your bowel. If it's too thick it won't spread out into your intestine. That has to happen so the glycerine will do its job.
Pour the mixture into a 2 ounce mini-aspirator bulb and gently squeeze it into your bottom. You are now committed! Nothing you can do can stop you from having an uncontrollable bowel movement. The longer you can resist, the larger will be the volume of poop, and the mushier it will be.
What's happening are two things: When the in-solution Metamucil starts warming up in your body it starts to swell, becoming a thick gel. The longer you can hold out, the more gel will be in your bottom. At the same time the glycerine is pulling water out from you intestinal wall and making your poop soft. Also, the glycerine irritates the bowel and gives you a strong feeling of needing to poop. Eventually, the bowel will start to contract on its own. You will be able to resist for a while, but eventually you will forcefully expel everything.
I sometimes do this and take a walk around the block. I don't know when I'll have to go. Most of the time, though, I give myself this enema, pull on my diapers and plastic pants, slip into and old nightie and lay down on the bed. I resist as long as I can, but when I finally fill my diaper the head-to-toe sensations are exquisite.
Enjoy!