When my utensils & plastic get stained from tomato sauce, I use Fantastic With Bleach. I let it soak for a while (sometimes I have to do it more than once) wash it & rinse it well & most of the time, the stains come out. Worth a try. I buy my Fantastic with Bleach at WalMart. Probably bleach diluted with a bit of hot water may do the same thing. I don't buy a lot of bleach so often times I don't have any.