The Premium Roll n Clean Self Cleaning Litter Box, Regular size is quick and easy to use. The Roll n Clean features a patented sifting grate that separates clumps from clean litter and deposits the waste into the pull out drawer. Simply roll the litter box onto the top and back again and the litter box does the rest of the work separating clean litter from the waste. The Large size is suitable for bigger cats or multi cat households.