The easiest way is to just heat up the banger and then inhale. Sometimes the oils as the banger is cooling flow up the walls and into the holes. Heating it up will help melt the oils and allow you to inhale.
Another idea that came our way from a user is that they inhale slightly when using the torch on it.
One can also use a small wire to put into the hole when it is warmed up, and then also inhale with the marble on top to make a vacuum in the banger