So you would like to allow your cats to access your rooms even when their doors are closed? KittyKorner can help. It is a hinge that turns any door into a pet portal. You will be able to use this to give your pet access to their litter box while managing odor better.
You simply have to make one simple cut to your door to get started. KittyKorner works with hollow or solid interior doors. It comes with template, and everything you need to get started.