Soak beans overnight in enough water to cover them. Next day, bring beans to a boil. Cut salt pork in cubes. Put 1/2 the salt pork in bottom of bean crock. Put beans and onions in crock and top with other half of salt pork. Mix molasses, ketchup, dry mustard and salt in a cup of hot water; mix well and stir into beans. Bake at 275F for 5-6 hours until beans are brown. Add water to beans if needed throughout the baking, so they don't dry out.