In a large pot, combine the broth, water, ham hocks, garlic, vinegar, sugar and red pepper. Bring to a boil over medium-high heat. Add the collard greens in batches, covering the pan and waiting for each batch to wilt before adding the next batch. Transfer to a 3 1/2 quart slow cooker. Cover and cook until the greens are very tender, 4-5 hours on low. Remove the ham hocks, remove and discard the skin. Remove the meat from the bones, coarsely chop the meat, and return to the slow cooker. Season the greens with salt to taste.