Rinse beans and soak overnight. Drain water and add 8 cups water to beans. Bring to a boil; reduce heat and simmer, covered, for 1 1/2 to 2 hours or until beans are tender. Drain beans and reserve liquid. In crockpot combine drained beans, onion, and salt pork. Add 1 cup drained bean liquid, molasses, brown sugar, dry mustard, pepper, and salt. Cover and cook on low for 10-12 hours or on high for 5-6 hours. Stir before serving.