what is the best thing to use to backflush your rad? I have some junk in there, it is soft I tried the prestone fast flush it did not clean it at all thaks in advance, Marty

Probably needs to be "boiled" out. Take it out to a professional for complete cleaning if you have materials left behind after conventional flushing.

Your not running enough corrosion protection or something is chemically going on in your radiator. Figure this out for longivity sake.

the best thing I have found is cascade dish washer soap put it drive it around and then flush