Roger explains this off and on in some of his videos. Basically find a plastic wax/scratch remover for car headlights and give it a good rub-down. He uses something they have in UK called T-Cut (or Teacut?) Wash the bin before polishing of course. It will just fog up again but the wax does help. What happens is all the grit and dirt swirling around in the bin will slowly scratch it up over time until it hazes over.