Look at the plus side, ericmason - 5% glycerin is a much cheaper enema than 20%!
This is true.
You can go through a lot of glycerin to get the percentages up even with fairly nominal enema volumes. Last night I upped the percentage from 10% to 15% (with less Ivory soap than I typically dissolve). The first choice you have to make is how much volume are you going to mix. I chose a 4-liter enema volume. To make a 15% solution takes 3.4 liters of water and 600 ml of glycerin. If you are buying it by the quart, it still consumes a significant portion of the bottle to make a 4-liter enema.
The next choice was how to introduce the solution. I chose to use one of my long, CT75 colon tubes to introduce the solution high up into my colon and then have it flow back towards the rectum. They have fairly substantial retention balls on them. Unfortunately, I couldn't get my longest one to make the turn at the hepatic flexure even with the introduction of the enema solution to help lubricate that turn (and I won't force it around that turn if it won't allow me to even with a few minutes of working with it). I went with the next best option which was to introduce a nominal volume up high, withdraw the tube and inserting the double balloon retention nozzle to continue the filling process. After allowing about 1.25 liters to flow into me, I pulled the tube, inserted the lubricated balloon nozzle and inflated it. Practically no leakage at all.
I then opened the valve, adjusted it and began filling from the bottom up. The flow slowed considerably as I approached the 3-liter mark because the internal muscle contractions had begun. And yes, @ericmason, there was a more definitive "burn" at this level. Not unpleasant or even painful. Just present in an interesting way. Opening the valve further didn't seem to increase the rate of flow in any substantial manner, so I manually pumped in most of the remaining solution leaving less than half a liter in the bag (note I didn't want to have to purge the air out of the tubing and the pump for the rinse and the rinse would sufficient dilute down anything left in the bag and hose). I was very comfortably full of this nice warm solution that was giving my an interesting "burn."
Let me also say that the nature of the contractions at 15% strength were completely different than those at 10%. At 10%, I am aware of "waves" of contractions traveling down the length of my colon "pressurizing" and then releasing the pressure in my rectum where the balloon is fully inflated and seated inside of me. Since the liquid does not compress, the sense of pressure to expel can be quite intense and can (and has) push the inflated balloon out of me when seated. When the pressure of the wave releases, the sensation is one of all the liquid/solids that the wave tried to bring down through my rectum "flows back" through the equalization of the pressure in the colon until the next wave comes.
At 15% there weren't a lot of distinct waves of muscle action in the colon. Instead, there were more random and more constant contractions (spasms) throughout the colon particularly in the transverse portion where I initially introduced the solution. It was more like "cramping" that you get from having diarrhea during influenza or a mild case of food poisoning, but much, much milder. Not terribly powerful or painful. And because there was not this continuous build up of pressure waves and a sense of urgency to expel, I was able to retain the enema solution a lot easier than at 10% strength. I was surprised when I looked at my watch and realized that I had already held this solution inside me for 22 minutes. I didn't realize that much time had passed. There was a temptation for me to see just how long I could hold this solution or how long before the contractions formed up into waves of urgency, but there was something else going on internally.
I experienced a very interesting set of sensations with my first 10% glycerin enemas and they had been smaller volumes (generally 2 liters; 1.8 liters of water, 200 ml of glycerin). Once the solution was inside me and the contractions began to build, I would position myself to begin masturbating with a nice slow stroking action. The double balloon nozzle fits my anatomy in such a way that the upper end of the nozzle and the pressure of the inflated balloon move to stimulate my rectum near my prostate when I'm stroking myself. In and of itself, it is a very pleasurable feeling and lasts as long as I continue to stroke myself. The rectal walls tend to pulsate with this stimulation and I've felt a similar effect with my largest glass butt plugs where the muscle action is not so much the urge to push the plug out as it is that the rectal muscles are stretched out enough that they can't really push the plug out without help and they "quiver and pulsate" in a mild way.
What I discovered with the 10% solution is that once the first colon and rectal muscle contractions begin, I can begin masturbating with a nice long, slow stroke and that stroking action changes the angle of the nozzle and balloon pressure internally on the muscle walls stimulating the areas around my prostate. I need to take my time and not hurry towards a typical orgasm. It takes a few minutes to get the stroking action to provide enough internal stimulation to synchronize with the muscle contractions associated with the urge to expel. At some point, I can stop stroking and allow the internal muscle action take over and sustain the internal stimulation. The intensity builds with time as does the urge to expel and what I experience is akin to prostate milking without the continuous flow of seminal fluid that I experience when I stimulate my prostate with a vibrator. Usually what I experience is intense internal muscle contractions that I cannot tell are the actions of the glycerin or something else. If I time it right, I can stroke myself to an orgasm that radiates from inside out. Immediately after that I have to pull the plug and deflate the balloons to begin the process of emptying myself out.
Since I didn't get distinct waves of contractions with the 15% solution but a rather constant level of less intense contractions and with nearly 4-liters inside me, it turned out to be rather easy to set up this self-sustained, hands-free internal stimulation. This one reason I think so much time passed (I wished I had videoed this session so I could go back and see my reactions and what I was doing). After 27 minutes of holding this solution, the internal orgasm (or assgasm, if that was what it was) was so intense that after it passed, I just had to release the balloons.
The expulsion occurred in a fairly predictable fashion, though more intensely and more completely. And rinsing was more difficult than usual because my internals were still tingling and sensitized by the experience.
I slept very deeply after last night's session and this morning was aware of the dehydration effect of the glycerin. I also feel extremely well cleaned out.