oops sorry I thought the pics told the story. There is a pane of plexiglass installed in the lower window opening. There is a small pet door installed in that plexiglass pane. The pet door leads into an enclosure that houses the litter box. The litter box is outside the house. No dust and no smell inside the house. There is a door on the enclosure for access to the litter box when litter needs to be removed/added.
Good for indoor cats only. The main drawback is you lose one window and you probably wouldn't want to use a window near any areas used for entertaining guests
This one works well enough but the enclosure could be as simple or as ornate as you wish. Your cat might appreciate a roof too for rainy days
Just a thought.