Place ox tail (4 pounds beef oxtail) and trimmed fat in a large cooking pot with 8 cups water (or water/broth) over high heat and bring to a boil, skimming off oil and foam as needed.
Reduce heat to medium and add salt, garlic and ginger (add onion now if used).
Simmer for 3 to 4 hours, skimming as needed (until meat is almost falling from bone and broth is a milky color). (If used, add sliced Daikon about ten minutes before end of cooking.)
Remove the soup from heat.
Remove ox tail from broth with a slotted spoon and place into serving bowls.
Using a hand held strainer, remove onion and garlic solids from soup and discard. (if used, add noodle to serving bowls.)
Garnish and Serve.
Chop the green/spring onions (if used, thinly slice the garlic cloves from top to bottom).
Ladle soup into serving bowls, add garnish, and season with sea salt/pepper to taste.
