For one, Slinky is extremely clean and neat. She kicks sand off her paws before she exits the litter tray, but Sayang and Scooter just leap out of it, trailing sand litter all over the kitchen floor. So we switched to bigger litter pellets, brands of which are Green Sign and Trustie. They can be seen here:
This is Slinky's very own toilet now, housed in our bathroom. Because she has stopped wanting to share her toilet with Scooter and Sayang. We placed our existing litter tray there, and bought a new one for Sayang and Scooter to share in the kitchen.
We then switched to pine pellets for their litter, which is even better, because it really eliminates odour, and works better with this new litter box, as seen here:
This is the bottom tray, which the top tray filters down to. In this bottom tray, the dust and pee and subsequently the smell is contained below, making it cleaner and less dusty in the top.
And we have a lovely clean-up system too, seen here are the scoops, the broom and dustpan and the air freshener (right) which we use whenever they have just pooped.
This toilet arrangement for our cats will likely be the status quo for a while from now. I can't wait till we buy more cat litter, it really is great!