When I did mine, I first took an old milk jug, rinsed it out, took a large measuring cup and poured 1 qt. in and marked it with a Sharpie, another qt. and so on. At drain time, I put a funnel in the jug and pulled the drain plug at the back of the pan and waited for it to finish draining. About 3.5 qts will drain out. There is a very thorough cooler line fluid exchange procedure at tacomaworld.com that I and many others have used successfully. I did mine at just under 41k on the factory fill and pulled the pan and cleaned everything out. There is about another quart sloshing around in the pan so be careful if you remove it...ask me how I know. Overkill probably but I got all the break-in junk out and put a fresh filter in it. Mine was about 1/2 qt low from the factory following the whole temperature check procedure. I used a scantool to verify the fluid temp.
