Pick over the dried navy beans, removing any stones or shriveled beans, then rinse them well. Place them in a large bowl, cover generously with water, and soak for 8–12 hours or overnight; drain and rinse before cooking.

For more reliable tenderness, transfer the drained beans to a saucepan and cover them with fresh water. Bring to a boil, simmer for about 10 minutes, and drain.

Add the beans, bacon or salt pork, chopped onion, molasses, brown sugar, dry mustard, black pepper, and water to the slow cooker. Stir thoroughly so the sweeteners and seasonings are distributed throughout the beans.

Check the liquid level before covering the slow cooker; it should cover the beans by roughly 1 inch. Add a little more water if needed, remembering that the beans will absorb liquid as they cook.

Cover and cook on LOW for 8–10 hours, or use HIGH for approximately 4–5 hours when you need a faster setting. Stir once or twice if convenient, and add water if the beans look dry during cooking.

Taste the beans near the end and adjust the salt carefully. Bacon and especially salt pork can contribute considerable salt, so it is best to wait until the beans are tender before adding more.

Turn off the slow cooker and leave the beans uncovered for 10–15 minutes. This resting time allows excess moisture to settle and the molasses sauce to thicken around the tender beans.