I want to Flush the Radiator today. I have 30K miles on it. Should I just drain and re-fill or should I Flush it. I was thinking of using this Prestone Super Flush that they got at Auto Zone. Does that stuff work. Also I heard that to drain it, in order to get all of it out the car need to be hot. If its cold then not all of it would Drain... Is this correct and if so, should i just drain it once i get home from work? How do you use the flushing chemical?