Cover beans with cold water by 2 inches in a large bowl and soak 8 to 12 hours. Drain in a colander.
Transfer beans to a 6- to 8-quart pot and bring to a boil with 8 cups cold water, broth, tomato paste, onion, and 2 tablespoons garlic. Put celery, thyme, bay leaf, cloves, parsley sprigs, and peppercorns in cheesecloth and tie into a bundle with string to make a bouquet garni. Add bouquet garni to beans, then reduce heat and simmer, uncovered, until beans are almost tender, 45 minutes to 1 hour. Stir in tomatoes with juice and simmer until beans are just tender, about 15 minutes more.
Prepare duck and sausage while beans simmer:
Remove all skin and fat from duck legs and cut skin and fat into 1/2-inch pieces. Separate duck meat from bones, leaving it in large pieces, and transfer meat to a bowl. Add bones to bean pot.
Cook duck skin and fat with remaining 1/4 cup cold water in a 10-inch heavy skillet over moderate heat, stirring, until water is evaporated and fat is rendered, about 5 minutes. Continue to cook, stirring frequently, until skin is crisp, 3 to 6 minutes more. Transfer cracklings with a slotted spoon to paper towels to drain, leaving fat in skillet. (You should have about 1/4 cup fat; if not, add olive oil.)
Brown sausage in batches in fat in skillet, then transfer to bowl with duck meat, reserving skillet.
Make bread crumb topping:
Add remaining tablespoon garlic to fat in skillet and cook over moderate heat, stirring, 1 minute. Stir in bread crumbs and cook, stirring, until pale golden, about 2 minutes. Remove from heat and stir in chopped parsley, 1/2 teaspoon salt, 1/4 teaspoon pepper, and cracklings.
Remove bouquet garni and duck bones from beans and discard, then stir in kielbasa, duck meat, remaining teaspoon salt, and remaining 1/4 teaspoon pepper.
Ladle cassoulet into casserole dish, distributing meat and beans evenly. (Meat and beans should be level with liquid; if they are submerged, ladle excess liquid back into pot and boil until reduced, then pour back into casserole dish.) Spread bread crumb topping evenly over cassoulet and bake, uncovered, in lower third of oven, until bubbling and crust is golden, about 1 hour.