Rinse & sort through beans. Place them in the slow cooker and add enough water to cover. Cover and cook on high for 2 hours, or until just tender. Or, soak the beans overnight in water to cover, then drain, rinse, and transfer to the slow cooker. Add water to cover.
Add the onion, bacon, molasses, maple syrup, cloves, ginger, and dry mustard to the slow cooker. Cover and cook on low for 6 to 8 hours, until the beans are very tender. Stir in the salt just before serving. (You may want to place the lid slightly ajar for the last 30 minutes of cooking time to concentrate any liquid and allow the top to caramelize.)
Transfer to a serving dish and serve immediately.