Why can’t cat litter be made washable? The litter could be made of non-clumping, small plastic, bio-degradable, odour absorbing beads, looking much like Fresh Step Crystals, that are washable. Rather than throwing litter away every day or so, you’d just rinse it off in detergent, let it dry, and put it back in to the litter pan. Buy a new bag of washable litter once a year to replace the litter that has been lost due to the cats tracking it through the house, or when you were scooping out the clumps of kitty poop.
There could even be special kitty litter pan, much like the automated ones that exist now, that wash, dry and recycle the cat litter automatically.