In the same Dutch oven, melt butter over medium heat. Add onion and garlic. Cook and stir until onion is tender but not brown. Sprinkle flour over onion mixture; stir to combine. Carefully stir in drained beans, sausage, ham shank, black pepper and 6 cups fresh water. Bring to boiling; reduce heat. Simmer, covered, for 1-1/2 to 2 hours or until beans are tender, stirring occasionally.