The Insight Clean Water Silo 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 gauranty 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 with no mess and easy refill. Dishwasher safe and available in green, yellow and blue.