Coffee enemas have been my favorite for nearly twenty years. I have always found them to be soothing and never irritating in my personal experience. Currently, I generally use them four or more times a week. A full pot of coffee from my automatic coffee maker conveniently produces two quarts - equal to seven full drinking mugs - so I use seven units of ground coffee per pot; however, I fill the water reservoir of the coffee maker with slightly under three pints and add the full amount of grounds, then top up the brewed amount to a full pot of two quarts with cold water, so that it's instantly ready for use at the most comfortable temperature for my enema.
Although I sometimes prefer the rush of a fast-flowing enema, with the coffee variety, I almost always take it at a slow rate by hanging the bag low and closing the clamp over the tube to one side, allowing a slower flow around the edge of the clamp. I vary the flow to last anywhere from ten minutes to almost an hour, then retain it another ten to thirty minutes.
Once I've taken all the coffee solution, I fully open the clamp while I'm holding it and, fully relaxed as I lie, allow backflow to occur to relieve any pressure that might develop.
I don't recall the source, but I've read somewhere that caffeine administered by enema has a completely different effect in that it is basically unaltered chemically in the body, whereas, caffeine that enters the body orally undergoes the normal digestive process that alters it in a chemical way that produces the undesired effects of caffeine.