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This is my first post. I'm new to this drain & refill procedure where you leave 60% of the old fluid in the transmission or repeat the drain & refill three times after driving 10 miles between each change.

Is there a reason why you can't flush the transmission by disconnecting the ATF warmer hoses or hose going into the ATF filter and holding them in a bucket while your friend starts the car (shifting thru the gears) until 3 quarts come out & you have them turn off the engine. You then add 3 quarts of new fluid back into the transmission & repeat procedure until you removed the 6.1 quarts of old fluid. Add the last 3.1 quarts of new fluid back into the transmission, reattach the warmer hoses and your good to go. I didn't include every step like jacking up the front of the car & placing in on jack stand or the possibility of a hose extension to reach the bucket. I'm more interested in if this will work.

This way you don't have to waste money on gas, washer or your time.

 
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You might run the risk of damaging the pump by having the engine running, and damaging clutch packs by not having sufficient fluid pressure. I'm just guessing here.

Also, aerating the fluid as the pump cavitates.

God put a simple drainplug on the bottom of the trans for a reason. Seems like a no-brainer to me.
You don't HAVE to replace the washer if you are careful, but it is recommended, of course.