Any Good Methods ?

Im not sure about in your area,but here,i carry them to my local radiator shop to get boiled out.They always come back looking like new when done.Im not sure what they use,as far as chemicals,but they are very shiny inside and out when i pick them up.The local guy here even has a way to shoot some compressed air in them to pop dents out,unless there too dented.Just a thought for ya