Includes a set of four casters which can be removed if not needed. Casters can be adjustable to aid in unlevel surfaces. Each unit has a polyethylene (hard plastic) removable floor grate over a slanted floor which allows dog waste to flow down a channel in the back of the unit into a plastic waste container at the bottom front of the cage. Waste will wash down into the front waste drawer. Simply light hose each cage and empty one waste container!