Doubt Purge Manguito Aerotherm Circ. refrigerant?

I have a meganeii 1.5 DCI Motor K9K P732 (2004). I have changed the coolant, without any problem, everything is perfect, using only the purge at the thermostat level. It turns out that in the aerothermous exit mushy there is a reinforced rubber thickening with an embedded element (I do not know if it is a valve or a purge) and a manipulable thread as a hardened rubber and with endive for flat screwdriver, which the K9K workshop manual calls a pothogue. Here is the problem: that I have no idea what it is or what it is for, because for more laps that I give, it does not open, neither nor na de na. I would greatly appreciate this doubt. Thank you so much.

It is a water system pothar