Replacement ScoopFree Trays come with a bag of crystal cat litter and a large glossed cardboard box designed to fit perfectly underneath the ScoopFree Original and ScoopFree Ultra. Slide your old tray out from under the ScoopFree unit, cover with the lid provided and dispose of the tray. Open your new tray and fill it with the crystals provided. Slide the tray underneath the unit. Reset your health counter (for the ScoopFree Ultra) when changing the tray to keep track of your pets use! Convenient, easy replacement! Never touch your cat's litter! Includes lid for hassle-free disposal Lasts for approximately 4 weeks for 1 cat.