65 cuda 318 radiator question

1965 cuda, 318 v8.

Any thoughts on why my radiator wont drain when I twist the little wingnut at the bottom? It drips a little, but doesnt actually drain. Am i going about this wrong? Or is there just too much crud at the bottom, and, if so, how do I fix that? I am trying to do a full flush, the car has been sitting for 9 years.

Thanks