Drain from the radiator pet cock. I did it myself. All in all, with the external low/high tank coolant tank included, it took exactly 1 gal. I did it at 60k miles; I regret doing it because the fluid came out crystal clear. I should have done it later at 100k miles. But now I know how to do it. I did not have issues with bubbling or air in the system.

 

60k miles and still clear? That's amazing.

 

Indeed! I am very impressed with these engines. I did not hear one water pump complaint on the forum so far.