In a medium size bowl, mix soup and milk with a whisk until smooth. Add drained tuna and macaroni. Stir until thoroughly combined. (Mixture will be thin.) Pour into a casserole baking dish that has been prepared with non-stick spray. Cover loosely with foil and bake at 350 degrees for 35 minutes. Uncover and top with crushed potato chips or bread crumbs. Bake uncovered for 5-10 minutes until macaroni is tender.