In a large pot, bring the meat, onion, optional radish, and garlic to a boil in 14 cups of water. Reduce the heat to medium, and skim off the scum. Boil, covered, until the meat is tender enough for shredding, 1 to 1-1/2 hours. Pull a string of meat off and check the tenderness. Remove the meat and cool. Discard the vegetables, reserving the stock in the pot. Spoon off any visible fat.