In a large pot over high heat, combine the beans with water to cover and bring to a boil for 10 minutes. Remove from heat but let sit for 1 hour. Drain beans and place them in a slow cooker. Add the ham hocks, onion, brown sugar, maple syrup, salt and water.
Mix well, cover and cook on high setting for 4 to 5 hours, stirring occasionally. During the final hour of cooking, add the tomato sauce and mustard, remove the ham from the hocks and discard the hocks. Mix well and serve.