>
> Please note that my "system" involves working with hot coolant under
> pressure and may present some safety hazards.  Eye and hand protection is
> strongly recommended.

Alternately, one can (with the engine cold and not running) plug a piece of
clean fuel line onto the pressure cap overflow nipple and blow into it until
only coolant comes out the front. Not very sophisticated, but it'll force
the bubble out of the radiator pretty effectively.
--
John Bange
'90 Vanagon - "Geldsauger"