for the people having problems with filling the flame king tanks are you making sure the notch on the filler is lining up with the notch on the tanks? if you dont do that then they will not fill. ive never had a issue with all 6 of my tanks and ive filled them all many times but you have to make sure the things are lined up.
as far as the fuel keg problems i cant help with that as ive never used those