Drain the bones. Wash the bones under running water. Clean the pot. Return the bones back to the pot. Add 8 cups of water, the onion, garlic, ginger and scallion. Bring it to a boil. Continue to boil, uncovered, for 10 minutes over medium high heat. Reduce the heat to medium low. Continue to boil, covered, for 50 minutes to an hour until the meat is tender and the broth is milky.