The Insight Clean Water Silo Tall Waterer remains on the outside of the cage while the extending water cup goes between the bars and into the cage. The Base screws onto the cage to guarantee a secure fit on horizontal or vertical barred cages. This Waterer has a patent pending valve to prevent leaks. The perfect waterer for everyday use or for the occasional weekend get a way with no mess and easy refill. Dishwasher safe.