Tuning Vulcan 3 Long. How to take out all air preassure.

I need to take out thenregulator of my Vulcan 3 long. 30 Cal in order to check what could be wrongnwith the regulator. 

I know it has a screw perfectly identified to take out the preassure of the the bottle.

What I do not know and would appreciatenyour help is how to take out the preassure in the plenum after having lost all preassure of the bottle.

I will appreciate your advice. 
 
I already had to order a Huma regulator for my Vulcan III .30 Cal.

The one that came with the rifle did not work at all.

Dang.



My Vulcan 3 the plenum pipe was made wrong ( location of breather hole ), and as a consequence the gun was assembled without the reg spacer ring.

Unless a sub 12 have another setup but i dont think so.

These are not inconsequential errors,,,,, i worry for AGT