Tomato sauce stains just about anything it contacts, including clothing and plastic. Even if you wash the plastic immediately, often a faint stain lingers. Scrubbing with scouring cleaners or pads will only roughen the plastic, making the item even more prone to staining later. A more powerful and inexpensive solution for removing tomato sauce stains lies in some basic household cleaners.
Rinse the item with cold water (hot water may cook the stain into the plastic, making it more difficult to remove). Put on rubber gloves. Fill a liquid measuring cup half full of cold water and half full of household bleach (be careful not to splash the bleach when pouring).
Use a sponge, dipped in this solution, to wipe down the stained item if it is a flat surface (such as a plastic cutting board); otherwise, if the plastic is a bowl, pour the solution into the bowl. Make sure the solution covers the stain--you may need to add more bleach and water until the bowl is filled.
Allow the bleach and water to remain on the stained area until the stain is no longer visible (this can be from ½ an hour to several hours).
Wash the plastic with dish detergent and warm water and rinse well. If the item is dishwasher safe, you can just wash it in the dishwasher. Check the manufacturer's instructions before doing this, however, as many plastic items will melt in a dishwasher.