Well, I poured in enough straight vinegar (not distilled) to cover the stains.

Later I added baking soda....it fizzed like mad!

Then I took it to the bathtub - sprayed Fantastik on it and left it for a while. Then I got the Comet with bleach, a plastic scrubbie...then switched to an SOS pad, and it's WHITE again!

USE RUBBER GLOVES!

Thanks, everyone!