I've got an empty radiator which I'm going to add some inhibitor to before filling. I'm going to add it through the blanking plug side, what size are these blanking plugs as I want to put on an elbow where the plug was with it going up to a piece of pipe then a funnel to fill it through? Also for the air to escape do I need to completely remove the bleed nut on the other side or just use a key & loosen that?