This cap for the Alphacool Core 200 series of reservoirs features 8 nozzles which are angled in such a way so the water pressure creates some sort of vortex in the reservoir. Simply saw off the top and press it on. Done.

The nozzles are twice times bigger than the factory ones.

Be aware though that when the water level is inadequate, micro bubbles and foaming will occur. The effect however is great as you can see here: