The coffee enema I take is to flush the liver. The coffee solution goes into the rectum and sigmoid section and gets transferred to the liver directly (see COFFEE: THE ROYAL FLUSH). Only a small quantity of coffee solution is required, say 2 cups or less.
For this type of retention enema to work properly, your rectum and sigmoid section need to be clear of all fecal matter, which could interfere with the absorption.
So to cleanse the rectum and the sigmoid section I take a cleansing enema, 1 to 2 quarts depending on how impacted I am at the time. I have tried a lemon juice solution, plain water, saline solution but I have always returned to a soapsuds enema as being most satisfactory. No long retention, just in and out.