I have a white sink, what do I use to get rid of the stains?

I have a white kitchen sink. I assume that’s porcelain, but I could be wrong; I am not the person you would go to about that kind of information. It stains pretty easily with various foods, though none permanent – or so it seems! I cannot for the life of met get rid of them, but my cleaning crew can. But how? I don’t know. So, Fluther, what does one use to get rid of stains in a kitchen sink? I’ve used 409, Mrs. Meyer’s Clean Day All-Purpose, Soft Scrub, Kaboom, Mr. Clean Magic Erasers, and vinegar, all to no avail.