Septic Stains in Shower Pan

A few months ago our septic backed up. Every since then the shower pan has a stain on it that I can't get out. I've tried bleaching and scouring powders, oxyclean. Nothing has worked. I think that the pan is plastic, but it may be fiberglass. I always tape the drain up to prevent the cleaner from going down the drain and causing another problem. I sure appreciate any suggestions.

Some people have had good luck with a Magic Eraser. If the fiberglass has microfractures in it, you may never get it clean. that's a common problem with older fiberglass stuff that was not embedded in something like concrete, plaster, etc.

WOW....thanks for the suggestion. It took about three of the "erasers" to do the job, but it took it straight off. I did not have to use any other cleansers with it either, which is great so I did not get the septic system balance messed up. THANK YOU, THANK YOU, THANK YOU!!!!