This is a self venting cat box I built. It does have a bathroom fan inline but, that turned out to be overkill. I tapped into the vent stack for the tub while I was remodeling the bathroom. Also did all the tile and everything else, really.
The box emits no smell, the hallway down one side traps loose liter before the cats jump out and keeps the dog from getting treats. It was a blast to make.
Looking in from the back of the shelves during construction. There is a small closet that goes to the adjoining bedroom. I sacrificed part of the closet for shelves in the bathroom and the cat box.
Here you can see the pipes leading from a small bathroom fan to A dedicated vent pipe. That pipe goes up and through the roof. I added power to charge a cordless razor or curlers (do people use those any more?) The blue electrical box behind that pipe houses the timer switch.
NOTE: THIS IMAGE INCLUDES A CONNECTION TO THE BATH TUB VENT STACK. DON'T DO THAT! SEE CHANGES I MADE LATER AT THE END OF THIS SET!