I wanted to find you a few sites that I thought were really good information. One is a forum site that i can not link you to here the other is not so here it is

http://www.enematips.com/yourfirenhow.html

Bowel stimulating enemas may consist of water, which works primarily as a mechanical laxative, or they may be made up of water with baking soda (sodium bicarbonate) or water with a mild soap dissolved in it; sodium phosphate solution, which draws additional water from the bloodstream into the colon and increases the effectiveness of the enema, but which can often be rather irritating to the colon, causing intense cramping or "gripping"; or mineral oil, which functions as a lubricant and stool softener, but which often has the side effect of sporadic seepage from the patient's anus which can soil the patient's undergarments for up to 24 hours. Other types of solutions are available as well. In the past, castile soap was a common additive to enemas, but it has largely fallen out of use because of the risk of chemical colitis as well as the ready availability of other enema preparations that are perhaps more effective than soap -- but which are certainly more irritating to colonic tissues. At the opposite end of the spectrum, an isotonic saline solution is the least irritating and has a neutral osmotic pressure, neither leaching electrolytes from the body, as can happen with plain water, nor drawing water into the colon, as with phosphates, nor adding anything to the bloodstream. Thus it can be used when a longer period of retention is desired, such as to soften an impaction.

There is a lot of good information but the best sites are the ones that the information comes from people who play that way. They are out there. I do think that it is key just to go slow and learn how it feels. Everyone is different. I never had much issues with cramping but Masters Lil one had, so just take your time. Again for me how fast you let it come into you made the difference. I did find btw using a vibrator during the enema very very hot.