I have found that Oust air sanitizer works great! Just make sure the cats are not around when you spray it, and spray up to the ceiling. It has a light pleasant fragrance that covers the litterbox smell, but the fragrance fades fast leaving behind a clean smelling room and no odor of litter at all. I swear by it.

But I can't say it enough, make sure no cats are around when you spray! It says on the label that its "harmful to humnans and pets" (which to me is them covering their hinneys in case of a alwasuit in our sue-happy society ) But you need one spurt and its done. By the time the cats return its been filtered through the air and not settling like other heavy fresheners. I've been using this about a year now and nobody has shown any ill effects, but I use it with one spritz and go. I do spray a whole room for five minutes straight, etc. One spritz and that is really all you need. I'm still on can #1.