Wash and pick over beans. Put into crockpot. Add water, salt pork, salt and onion. Mix well so beans cover pork. Place liner in base. Cover and cook on low for 14-16 hours or until beans are tender.
Cooking time can be reduced if beans are soaked overnight then cooked on low 10-12 hours. When beans are tender, drain bean liquid reserving 4 cups. Combine reserved liquid, molasses, ketchup, brown sugar and mustard. Add to beans in liner; stir well. Cover and cook on low 6-8 hours longer.