Rinse out the plastic bowl with water. Dry it with a towel. Set the bowl in a sunny window or outside in the sun for two to three hours so the sun can bleach the stain.
Pour 1 tablespoon of cream of tartar into a bowl. Drizzle hydrogen peroxide over the cream of tartar. Stir the two ingredients together until they reach a consistency similar to cake frosting.
Spread the paste over the remaining spaghetti sauce stains in the plastic bowl. Allow the paste to dry.
Moisten a sponge with water. Scrub the inside of the plastic bowl to remove the dried cream of tartar paste. Rinse the bowl with water.
Wet the nylon mesh sponge with white vinegar. Sprinkle baking soda over the sponge. Scrub the plastic bowl to remove any last remnants of spaghetti sauce stains.
Rinse the bowl with water. Dry the plastic bowl with a clean towel.