This is the single most important quality of life improvement I've made since living in this house. I love our cats, but litterbox smell is the worst. When we lived in an apartment we kept the litterbox in a bathroom and let the bathroom exhaust fan run 24/7. This was better than nothing, but having to leave the door open so the cats could access the box meant that it wasn't completely effective at pulling the odor away from our noses, and it blew a lot of conditioned air outside, costing $$.
When we bought a house that has this tiny broom closet that's not super useful for anything else, I saw my chance. I designed a mount for a small blower so that I could duct the stinky litterbox air far away from me. The wall plate fits 1 1/4" PVC pipe that I ran through the wall down to the crawlspace below the living space. I chose the crawlspace instead of the attic because the run of pipe was much shorter and the crawlspace is open to the outside and has a dehumidifier in it already.
Alternatively the wall plate can be affixed to a piece of wood or plastic or cardboard etc. and can be shut in a window. That's what I did for the first few days before I ran the PVC pipe in the wall. I added a clamping pipe flange for the crawlspace end of the pipe to seal against drafts and bugs and hold the pipe in place while I installed the stuff at the other end.
The speed controller and excess wire for the blower should just get stuffed into the wiring trench in the blower mount. The connectors for the power adapter and the blower should be cut off and the wires installed in the terminal block in the speed controller. No pressing need to tin or solder them, unless you want to. Run a bead of sealant around where the blower meets the wall plate before attaching the blower/blower mount/electronics assembly to the wall plate.
I just leave it on set to about 40-50% of max. According to a kill-a-watt it's using about 1.5W and IIRC it's moving about 2cfm of air. Two indoor cats use the litterbox exclusively and we replace 7lb of walnut shell litter in it weekly. I have a repeating reminder set on my phone to change the litter because there's no evidence of it needing to be changed until the cats start getting upset about the state of the facility on day 8-9. (That only happened once or twice :-O )
Speed controller: https://smile.amazon.com/gp/product/B00RYKR83Q/
12V adapter: https://smile.amazon.com/Adapter-100-240V-Transformers-Switching-Adaptor/dp/B019Q3U72M/ (or any other 12V power supply that has UL/CSA/TUV safety approval)
Bilge hose: https://www.lowes.com/pd/EASTMAN-1-5-8-in-x-6-ft-PVC-Bilge-Pump-Discharge-Tubing/1000180583
Sealant: https://smile.amazon.com/GE-GE284-Silicone-Kitchen-Squeeze/dp/B000PSE46S/ (or any other household sealant)
(2) approx. 80mm lengths of 4.5mm or smaller threaded rod
(4) nuts for above
(4) #8 pan head mounting screws for the wall plate + anchors as applicable
(2) M4x16 socket head cap screws and matching nuts
(2) M4 or so screws + nuts to secure the litterbox-side hose adapter to the box lid
Tape/plastic as needed to seal up any vents in the litterbox lid