Tupperware is prone to getting stained by tomato-based sauces. Every time I put spaghetti sauce in one, it gets stained. If you want to clean the stains from your Tupperware, or any other plastic-based container, create the following mixture:

1/2 cup bleach
1/4 cup baking soda
1 cup vinegar

Pour this mixture into the stained container and let it sit for several minutes. No scrubbing is needed. If you have several containers to clean, once you are done soaking one, pour the mixture into the next and repeat for as many as needed.