I went 15 years, even took the tranny out for rear main service once, and swore there was not a drain plug on this model.
However, there is, I finally found it. It's up on the back side of the converter about an inch up the curved surface. It looks just like the pan drain plug, uses a 5 or 6 mm allen. The plastic plug is just to hold the converter in the tranny during installation. The drain plug is not above the plastic plug, but rather about an inch farther back. So turn the front crank pulley bolt with a big socket (15/16 or 1 1/16, can't remember exactly) and look up behind the plastic plug (toward the rear) as the converter turns, and you will spot the drain plug.
Between that and the pan, you get almost all the fluid out, about 8 qts I think.

DG