Optimize Transmission Flush

Because the pan only holds about 3.5 quarts, doing multiple drain-and-fills ends up wasting a lot of new fluid—each cycle mixes old with new, then you drain some of both.

Smaller drain/fill amounts are actually more efficient in terms of how much new fluid stays in the system. For example, if you did an overfill-style flush with:

• 8 qt per cycle: you'd need ~24 qt to reach 80% new fluid
• 4 qt per cycle: about 20 qt
• 1 qt per cycle (just for fun): only 18 qt total

I’ve seen people flush through the transmission cooler lines. Is there any chance that method works more like a “plug flow” system—where old fluid is pushed out while the new fluid stays unmixed? Or does it still mix inside the trans before exiting?