If it's the 5R55, I used a 1/4" brass NPT fitting with a hose barb on one end to thread into the center drain plug. I then used a fluid pump for an outboard lower unit to pump from a gallon jug of Maxlife to refill. Worked great. No need for the expensive special tool, as the pump keep pressure on the fluid so it wouldn't drain back out of the trans.
It also works great to pull a line off of the cooler in the radiator and have the trans pump itself empty and then refill. Repeat 2 more times for a full exchange.