Replacing antifreeze in a 2004 MPV with rear heat/ac

What is the trick to replacing the antifreeze in a 2004 MPV with rear heat/ac. The capacity is a little over 3 gallons, yet when I drain the radiator, only about 1 - 1/2 gallons comes out.  How do you go about getting a complete drain of the system?

You are not going to be able to drain out the full 12.7 quarts of the cooling system unless you pull the engine and roll it over a couple of times dagresh. You can however drain out a significant greater portion if you remove the plug located in the rear heater pipes under the vehicle approx mid vehicle. See somewhat weak diagram below for a better idea of the location.


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