Very simple....an oral enema uses a salt solution....sea salt, Epsom Salts , magnesium citrate, etc....so that water is drawn into the bowel which results in rapid evacuation. Water and Sea Salt is a common oral enema as part of the Master Cleanse...and the Epsom Salt flush is commonly used during the liver flush.
If using an oral enema...make very sure to drink plenty of water before use and afterwards as they can be quite dehydrating...also replace loss electrolytes.