If retaining an enema is a goal, I do have some observations about what works for me.
First off, holding an enema is a sort of "enema masochism." I don't ever deliberately hit my thumb with a hammer or willingly cause myself pain in any other way, but there is a masochistic facet to be found in my klismaphilia. Holding an enema, especially a big one, causes me discomfort, so why do I seek it? It must be related to why otherwise perfectly normal people submit themselves to the pain of a spanking, a component of submission that can sometimes bring tears. But without psychologizing the "why" any further, here is the way I do it.
Step one is a thorough clean-out beforehand. Trying to hold a lot of water in a colon full of poop is counter-productive and often messy. So I get the playing-field cleared before playing the game.
Posture is important. I lie on the bed, often in the reverse Sims position. Injecting the water high and slowly is a big help. Holding two quarts that has been injected low into my rectum is a very different sensation and challenge from holding that bagful when it has been injected high inside me through a colon tube. I make sure the tube is thoroughly lubricated along its whole insertable length, and I don't force it. I usually set a trickle clamp to keep a slow dribble flowing, which helps it get through tight spots and bends. Be careful with colon tubes; my hubby hurt himself that way recently. Once the colon is swollen with water it is usually easier to get the tube to go in deeper.
I use a super-plus tampon as a retention aid. Usually I insert the tampon first, then work the noz past it and let out just enough water to swell the tampon. A tug on the string to seat it, and it becomes a remarkable aid in "holding my water." The OB brand "Ultra" is my top choice for the purpose. If I do insert it after the enema is in me I do so on the toilet because there is almost always a leak when I do that. The tampon will squeeze down and come out easily with a steady pull on the string when desired.
Water temperature makes a big difference. I find a cool enema easier to retain than a warm or hot one. Cool, not ice water.
I put on a "retention garment" of some sort. As counter-intuitive as it may sound, a really tight girdle is a big help in retaining the enema. The one I usually use is tight enough it would drive me insane under a dress out in the world, but is perfect to help support the weight of water in my abdomen when I'm doing a "hold."
Walking will decrease my ability to hold the water. My usual practice when I'm holding is to sit at the computer and look through enema porn. Anybody else ever look at that stuff? I very routinely can hold two quarts for thirty minutes. Sometimes I hold it longer, just cuz I can. Two quarts is relatively easy for me. Going to larger volume rapidly increases the difficulty in holding. For me, to take four quarts is usually doable, but I usually can't hold that large an enema for more than a minute or two, even with a tampon and a girdle. Three quarts is kind of an in-between, much more difficult to retain than two, but doable for me. Three quarts will usually bring me to tears somewhere along the way.
I don't usually add anything to the enema water, but I do keep my electrolyte balance up with oral supplements. My all time holding records: I have held two quarts all night on several occasions. I did one time each succeed in holding three quarts for two hours and four for one hour. Why ask why?
Hugs,
Diane