I think you got PA LEMON there. Not to worry ... don't give up on flushing!
I have been used at least 12 PA120.3 and 6 PA120.2 ... yep! the white thing is there. Just connect the barb with garden hose and run the tap for 30min each inlet or outlet [best if your tap got hot water] It will run clear If you wanna to shake your rad ... make sure it's half full and full load of arm mussel! Good luck! Cheers!