How do you flush the cooling system on a 2003 Chevy Trailblazer?

If you must do it yourself ensure that you drain and capture all the old coolant. There is not a drain cock on the system. You must use the rad hose disconnect.

The dex coolant does not like air. It is well worth your while to get a shop with an evacuation flush unit to replace the coolant. This method pushes out the old coolant with the fresh stuff. Effective and mixed to the proper proportion to maximize the long life of the Dexcool.