What do you use to get rid of nasty stains inside the litterbox that just won't scrub off?

I usually clean the litter box with a mixture of bleach and baking soda(not used together) After the box is washed I fill it with bleach and water and let it sit for about 15 minutes and then rewash it and scrub it down with baking soda to take the bleach smell out of it. Sammycat hates the smell of the bleach and will not use the box then.

Soak it first in vinegar, let it sit in the vinegar for about 15 minutes, then rinse it off with hot water and the stains should peel right off. Or just go and buy a new litter box, your cat won't mind! :)