Place black beans and cover with 3 cups water. Let sit for 5 minutes. Discard anything that floats to the surface. Drain.
Cover black beans with 3 more cups water. Let soak, 4 hours to overnight. Drain.
Combine drained beans and 3 cups water in a rice cooker. Cook on the "Porridge" setting, adding more water if needed, until tender, about 2 hours. Drain.
