PetSafe ScoopFree Ultra Self Cleaning Litter Tray Replacement Litter Trays are disposable litter trays with leak-proof lining for easy cleanup. The crystal litter absorbs urine for 5x better odour control than other litter and uses 5-10x less litter than clay and clumping litter. UsageFor best results, replace the litter tray every 20 – 30 days for one cat, every 10 – 15 days for 2 cats, or every 7 – 10 days for 3 cats. You might need to replace the litter tray more often if you have senior cats, kittens, or cats who eat a diet high in crude fibre, ash, and by-products. This product is only suitable for use with the PetSafe ScoopFree Ultra Self Cleaning Cat Litter Box.