1999 Chevy S-10 drain my trainsmission fluid

Your tranny pan does not have a drain plug by design. The reason for this is that when you change the tranny fluid you should change the tranny filter also. This requires the removal of the transmission pan - removing the tranny pan is also how you drain the fluid (unless you purchase an after market pan with a drain plug).I suggest getting a transmission fluid/filter kit. They come with a new filter, pan gasket. Remove the pan bolts slowly with a large catch drain pan under the tranny. When re-installing the pan do not over tighten the bolts.

BTW - Draining the transmission fluid from the pan only replaces the fluid that is in the pan (about 5 quarts or so). Your transmission has 6 to 8 more quarts inside of it that will not be changed by just draining the pan. In order to TOTALLY change the transmission fluid (in any transmission) the transmission must be removed, along with the torque converter, and drained.