In a large skillet (cast iron preferred), heat the bacon grease or butter over medium heat until melted. Stir in the flour.
With a fork or whisk, cook and stir until bubbly and smooth, about 3 to 5 minutes. Do not burn the flour. You want it to be slightly brown and smell "toasty". (Trust me, you will smell it.)
Pour the liquid from the can of tomatoes into the grease and flour mixture. Whisk until thick and smooth. Crush the tomatoes (by hand) into the gravy mixture, adding all of the liquid. Add the pepper and salt.
Continue to stir. Add up to 1 cup of water if needed. Reduce heat, cook and stir until the tomato gravy has reached desired consistency.
Serve hot over warm buttermilk biscuits, rice, or grits.