Slow cooking allows the bacon, thyme and leek flavors to seep into the rice and red beans.
In a 5-quart slow cooker, combine beans, bacon, leek, celery, thyme, and 6 cups water. Cover; cook on high setting until beans are tender, about 4 hours (do not uncover while cooking).
Stir in bell pepper; season with 1 teaspoon salt and 1/4 teaspoon pepper. Cover; continue cooking until bell pepper is tender, about 20 minutes more.
To serve, discard bacon slices, if desired; stir in 2 cups cooked white rice.