That's the real beauty of a Rainbow-
As long as you are picking up "wettable" dirt (which cat litter is, since it soaks up the urine), nothing should ever get past the water basin (although large amounts of litter would probably just make a muddy mess in the basin). The two main things to avoid would be talc (baby powder), and fireplace ash. Those are "non wettable" and would then be sucked through the seperator and into the motor and hepa filter. The seperator keeps the water (and dirt) from being sucked through the motor. It is attached to the motor, and spins at high speed in the water as air is pulled through it. The spinning seperator churns the water, dissolving the dirt and keeping the suction path clear.
