Bleaching??

You can't use regular bleach on polyester--it will set the yellow. Try Oxyclean or Miracle White, both in the laundry section at the grocery store

Teri

I doubt you'd get very good results, that large a piece of fabric will bunch up, even in a commercial machine, and any product will have difficulty reaching all the bits. That said, you might take a look at the Rit products for color/stain removal:

Beverly

It this is a yellow polyester (instead of a stained polyester), you're pretty much out of luck. Poly is not dyeable by home methods, nor can you strip the color easily.

Kay

Thanks for the advice everyone, it's been very useful