As my wife and I finished off half of our basement as a living area, it became apparent that our furry little friends were creating a smelly situation. To combat this, I created a power vented litter-box system that can be built completely using hardware store supplies. It was hacked together in an afternoon but has stood up very well and works flawlessly.
The litter boxes themselves are large plastic storage bins with a cat-sized hole cut in the lid. The venting system is powered by a 4" low powered inline duct fan and the tubing is cheap dry vent hose. There is a damper to prevent back drafts (gross...) and the tubes are connected using foil tape. The fan is not powerful but creates just enough of a draft to suck the smell outside. The one downside is that our back porch smells a bit like litter box, but we do not use it often.