This is how I do mine:
I pull the transmission cooler return line, and let the transmission fluid drain that way—it allows you to get all the fluid out of your torque converter. Moreover, I drop the pan to change the filter and inspect and clean everything myself.
I got tired of dickering with service mangers. They want to argue with you and say you don't need to change the transmission filter because it is "good for the life of the vehicle"—yea, you can kick rocks with that stupidity. Moreover, I don't like the idea of flushing the transmission with a machine. Essentially you are pushing/blasting old fluid through your transmission, which could clog the valves and/or damage something due to the metal shavings/debris that is inside the old fluid. If you are going to flush your transmission, you need to at least drop the pan first and clean everything (including changing the filter), then flush it.
Do stuff yourself and know that it was done right.