PetSafe ScoopFree White Litter Tray Refill With 'Free' Crystals 3 packFree trays don't have a lid so they can nest, making them easier to stack and store in small spaces. Each tray includes a garbage bag for easy disposal. The crystal litter provides superior odor control and the tray includes a covered waste compartment that locks in odors, so you can leave the tray alone for weeks at a time. It is completely disposable for hands off convenience, so you don't have to touch or smell messy waste. After a few weeks,