Welcome rljjr.
rljlll- The whole idea of the airline to a PH is to keep air bubbles out of the tube, not pull the initial bubbles out. Was the line full of water when you connected it to the pump? Is there a tight fit of the airtube at both ends? Is the powerhead flow strong enough?
Plug in or glue in the airline and then suck the air out of the u-tube and line. When you get a mouth full of dirty tank water, you are good to go. Then connect it to the powerhead. I never had to do this with my old HOB overflow, but I do have an airline for my siphon between my tank and side by side fuge.