For older and less messy kittens, I collect the cardboard box 'trays' that cat food cans are packaged in, and use them as litterbox liners. They also fit the small standard-sized litterbox, and can be 'scooped' once or twice. When the box begins to get soggy, just throw it away with the litter inside it. This protective liner keeps the litterbox clean, and is biodegradeable and FREE!