use option 1
if you think about it in terms of where steam is in the boiler (at the top) and that is where the steam pipe would draw from. So if you fill till; water comes out the wand your boiler has to be full.
the GHead might draw water from the bottom of the boiler (or close to so it does not "run dry") there fore filling the boiler by just running the water will not "fill it"
hope that helps, I am glad you asked :)