1999 Chevy S-10 how do I drain the radiator

Hi, in the picture, the lower left, white valve. The picture is a replacement radiator, I'm not sure if original has the same valve? The coolant capacity for the 2.2 is 11.5 quarts, that may be engine block--radiator, everything. I fill the radiator, start engine, if coolant level drops out of site, I add more coolant. Now, if there is a procedure for opening bleeder valves, so air doesn't get trapped, I don't have that right in front of me. Follow manufacturer recommendations.