I am with GSXR...
The flushing is a two step process.... one is the Citric Acid ( specifically mentioned in the FSM... ( to be preferred ) I think is the way they put it... and they say you may have to use it more than once to be sure the flush can access the rust and grime buildup...
The idea is that you must get rid of any and all of the oily coating before whatever flush you use will be able to do its job correctly...