Place the pinto beans into a large container and cover with several inches of cool water. Soak beans 15 minutes; drain and rinse.
Heat bacon grease in a large pot over medium-high heat. Cook and stir salt pork in hot grease for 1 minute. Add onion, celery, bell pepper, black pepper, and chipotle powder to salt pork; cook and stir until the vegetables are soft, about 4 minutes.
Stir smoked sausage, bay leaves, parsley, and thyme into salt pork mixture; cook and stir until sausage is browned, about 4 minutes. Add garlic and cook until fragrant, about 1 minute more.
Stir beans into sausage mixture and add enough water to cover the beans. Bring to a boil, remove from heat, and transfer beans mixture to a slow cooker.
Cook on High for 1 hour. Reduce to Low and cook until beans are tender, adding water as necessary, about 6 hours more.
Mash about 1/4 the beans against the side of the slow cooker crock with the back of a heavy spoon. Continue cooking on Low until beans are tender and creamy, 15 to 20 minutes more. Remove bay leaves.