A baking soda paste is one of the best ways to remove tomato stains from Tupperware or other plastic storageware. A secondary solution is to bleach the plasticware, although this option is recommended only for the most extreme stains.
Scrubbing with a baking soda paste made of three parts baking soda to two parts water should remove most tomato stains from Tupperware. Avoid using scrubbing pads or abrasive cleaners. If the baking soda paste does not remove all of the tomato stains, let the Tupperware soak overnight in a warm water with a few drops of bleach. After the overnight soak, the Tupperware should be washed in the dishwasher to remove the bleach.
Tomato sauce stains are caused by the acids in tomatoes. This is the reason why tomatoes and spaghetti sauces are stored in glass. Cooking oil sprayed into Tupperware, or a light rubbing with olive oil before the container is filled, can protect the plastic from staining. However, this does not adequately protect the plastic against damage when the tomatoes are heated. Because the heat can cause chemicals from the plastic to leach into the tomatoes, the tomatoes should be moved to a glass container before they are heated in a microwave.