Roca Cistern

The chrome button in the center of the lid has an upper tank of lacking substance. This rod passes through a hole in the lid that is smaller than the chrome button, and is attached to the mechanism inside the tank. There is no obvious way to remove the chrome knob from the stem, then what? The tank is measured by allowing water to flow into the toilet bowl, so any ideas would be greatly appreciated.

try the website of the company http://www.roca.com/

I have no idea but good question!