Add the 6 cups chicken stock or broth and 4 cups water to a large slow cooker. Add the ham shank, sage, basil and garlic powder. Cover, turn the slow cooker to LOW, and cook 6 hours. Add onions, potatoes, carrots, celery, and the parsley. Cook another 3-4 hours, or until vegetables are tender. Remove the ham shank, returning any bits of meat left on the bone to the soup; discard the bone.
Drain beans (don't rinse). Take about 1/2 can of beans and place in a small bowl and mash. Add to soup and stir. Add remaining navy beans. Season with salt, cover and continue cooking on LOW 30 minutes longer. Ladle into soup bowls and serve hot. Goes great with garlic bread.