In a large pot, bring the meat, onion, scallions and garlic to a boil in 14 cups of water. Reduce the heat to medium low, and skim off the scum. Simmer, covered, until the meat is tender enough for shredding, 1 to 1-1/2 hours. Remove the meat and cool. Discard the vegetables. Stir in soup soy sauce, salt and pepper to taste.