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.

Step 1:

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!

Step 2:

Here is the timer from the front. At one point I was going to put a motion detector in the box. Glad I didn't because there seems to be a natural draw in the box that self clears the air. Not enough to pull heat out of the house. Just a slow steady flow to removes stink.

Step 3:

The box is coated with shellack. Shellack resists soaking in any odor and it's waterproof. On the floor of the box I poured about 1/8" of epoxy in case of spills. The finished box can hold water. 2 inches deep (just had to try for fun)

Step 4:

The box rests on 4 100 pound rails. It weighs about 35 or 40 full plus a 20 pound cat. The rails extend out quite far. The hardest part of the project was building a nice square box inside another one with the right amount of space to accommodate the rails. I got lucky. the box slides out smoothly and does not tip at all.

Step 5:

I also added this neat set of pull out shelves since there is no medicine cabinet.

Step 6:

The "passageway" down the left there serves two purposes. That's a plastic door mat cut to fit in the channel. When the cats exit, they don't bring any liter back into the house -it actually works like a door mat should! It also prevents my dogs from stealing "treats" -they can't get their big Labrador heads in there.

Step 7:

When the drawer is shut, it works like a charm. I can open it to scoop into the toilet or replace the litter. I put the plastic liter box in a 3mm plastic contractor garbage bag and them fill the box over the bag. Just pick up the sides of the bag and turn it inside out. No mess!

Hope you enjoy

Fred

Step 8:

After seeing I've missed some level of detail (pardon, this is my first submission and I understand that I've taken much for granted), here is some detail on the venting architecture. The important item to see is the P trap at the bottom of the image in the stack that the box is connected to. This prevents dangerous gasses from getting into the home. Water in the traps seal the stack from allowing gasses into the home. The best way to avoid any possible issue is to have a dedicated vent stack.

NOTE: I RETURNED TO THE PROJECT AND ADDED A DEDICATED STACK. SEE NEXT STEPS!

Step 9:

Contrast on this image is tuned up to help see detail. After some consideration I re-opened the wall in the closet, disconnected from the vent stack and redirected the pipe for a dedicated vent stack of it's own. Typically a bathroom fan uses a four inch pipe but the volume of air being moved is small and the fan is very small so it won't be stressed. Larger fans require larger vents or you'll stress the fan. (Imagine a vacuum when you suck up a sock)

Step 10:

This is an image of the finished dedicated stack. I would have rather kept it in the wall but, that would have been a very invasive project! I sanded the outside of the ABS pipe to rough up the surface for best paint adherence. The box at the bottom contains the fan. Since the box comes so far into the closet, I just divided up the remaining space at the bottom with shoe shelves.