Crumble the slice of meatloaf into a skillet with the drippings. Add flour and tomato sauce and mix well. Add milk and continue to stir over medium heat. When mixture starts to bubble, turn to low heat and simmer for a few minutes. If it is too thick, add a little more milk. I'm guessing it should take about 10 minutes to put it together and cook it. Add salt and pepper if desired.