With drain plug, you can not change all of fluid. Also, CX9 does not use regular ATF. you should buy it at dealer or online. driver manual has information for fluid. i read an article before i changed my transmission oil said " no additive in cx9 fluid. use same type of fluid."
changing the transmission fluid
1- remove the air filter box
2- open the filler plug
3- lift the vehicle on level
4- open the small hex plug then open the leveler tube. ( i dont remember the sizes)
5- drain the fluid
6- close the leveler tube then small hex plug ( if small plug rusted, you may need to buy new one, mine seized)
7- fill around 5qt of fresh fluid and close the filler plug
8- adaptation: turn ignation on (with out engine starts), move the gear knob on each mode. R - N - D. every mode wait couple of sec. do it 2 times.
9- start the engine, press the brake pedal and do #8.
10 - drive the vehicle about 1 mile with low RPM and make sure use triptronic.
11- park your car and keep engine running.
12- lift the vehicle
13- open the small plug and get over filled amount.
14- until fluid comes out like spit out, then close the small plug
15- all done.