This 3 piece tray set helps your litter last longer! The Catmate Litter Tray Set aids in keeping litter fresher for longer. Using Catmate wood-based pellet litter, simply shake the top tray to let the dirty litter fall to the bottom tray, and your clean litter stays on top! We suggest emptying the bottom tray daily when you remove any stools from the litter tray, in conjunction with a weekly full tray clean.