1. A drain and fill uses the ATF drain plug to drop about half the ATF. Measure the collected fluid and add back the same amount of new ATF fluid via the ATF dipstick (which is the yellow one) hole with a long thin funnel.
2. The Gibbons method uses the ATF pump to pump ATF out of the ATF radiator line. Engine is run to run the pump, and stopped after 2 or 4 quarts are pumped out. I used 2 quarts at a time. Refill an equal amount to avoid the ATF level getting low. Then repeat until the ATF comes out of the line looking new. This method replaces much more of the ATF as the ATF system is used to circulate the fluid. You can shift the transmission through the gears, leaving at each one briefly, foot on brake during the process to try to remove the older fluid.
Take a quart container, fill it with water, and pour into a gallon container (plastic water jug). Mark the 2 and 4 quart levels on the gallon container then discard the water. Make up an extension hose and connect to the ATF radiator line. When the jug is full, you can put the used ATF into another, larger container.
IPD has a cheap kit for this with instructions:
https://www.ipdusa.com/products/4808/10 ... ipd-107945
3. There is a little confusion over the term "flush". There were some powered machines that forced ATF fluid through a transmission. This is generally accepted to be bad for the transmission. Now, most machines that are hooked up to an ATF circulation lines are more gentle and perform more of an ATF replacement action, similar to the Gibbons method (2 above).
Note. Some have recommended that for older transmissions, it is gentler to them to just do the drain and fill. But then to repeat the process after a few weeks or months. This dilutes the older fluid to 50%, 25% 12.5% and so on at each change.
There is a lot of discussion over which ATF is best. Take a look at XC70Rider's link above.
And check the AFT level, before and after the process. Best to do it after driving for about 20 - 30 minutes so the ATF is warm as it expands and the volume is temperature dependent! Watch your hands when reaching for the dipstick, a glove helps protect you from the hot pipes.