Heat oil in a large soup pot over medium heat. Add half of the garlic and half of the ginger and cook for one minute, stirring. Add the fish sauce, 3 tablespoons soy sauce, and 6 cups of water. Stir well and taste. Add a touch more soy sauce if it’s not salty enough for you (or a touch more water, if it tastes too salty). Cover, increase heat to high, and bring to a boil. Once it boils, reduce heat to medium and let it simmer while you prepare the won tons.