Very smart way to provide ponds without bottom Drains, bend fitting with a 32mm hole for tubing to eliminate a vacuum from being cased inside the system, the pipe allows the system to vent to the atmosphere. Comes with a hosetail 32 to 25mm for using 25mm hose to vent. The dome has a PE bottom plate so it cannot suck to the pond liner. Comes with a bag of gravel to weigh the dome