How do you drain the transmission?

New member here with a 2002 STS that I want to change the transmission fluid. Dropping the pan only releases 4 quarts of Dextron III. amd I've read that this trans (4T80E?) has a side resevoir that holds about another 7 quarts. From the bottom, I think I see it on the driver's side. Right along the side-bottom the the transmission case, there are 5 bolts with 13mm hex heads that appear to hold the side case. A couple inches above these are 2 bolts with 10mm heads and flat washers screwed into raised bosses. With the pan removed, I can't spot anything on the bottom of the trans that looks like a pipe plug to drain the side resevoir. Any chance these 10mm bolts are the drains? I sure don't want to start taking bolts out without knowing what they hold. By the way, I was suprized to see the "filters" for this trans are really only screens, not like the filters for other GM trannys I've cut apart. Any other tips or info will be greatly appreciated. :helpless: