Neither colonics nor enemas reach the small intestine, and I don't think you would want them to.
Enemas are typically used to relieve routine constipation and cleanse the descending colon, rectum and sigmoid portions, whereas a colon hydrotherapy treatment can comfortably cleanse the entire colon from rectum to cecum, removing old encrusted plaque on the colon walls in the process.
Each has their place. A gentle home enema can provide a convenient relaxing and healthy cleanse for virtually no cost, while professionally administered colonics offer a more thorough cleanse but at a greater cost.