Draining fluid from cooling system 99 blazer

:confused: On the Radiator I’ve found the petcock or release ,whatever you call it. Is there a tool to loosen it? It looks like an allen wrench but what size. Any tips on tool style to use and loosening the valve. It looks like working through the wheel seems easier. Also how much antifreeze is needed to refill the system?
Thanks
Larry
Where do you get rid of the old antifreeze?

lower radiator Pass side. Green plastic spade. All you need to do is turn it 90 deg. It will drain. It will also move outward when opened and you will need to push it back in while rotating ti to close it.



Regards,
Heli