As long as u fill up from the bottom of the drive,,,no problem. The air will go back out thru the res.
My Pump ,,,i bought in Walmart,,,for 9 bucks and worx 100 %,,,the bigger one i have ,,,( bucket pump ) is from harbor freight,,and also was cheap,,worx 100 %.
I think u need to check the pump u have,,and maybe replace an o-ring in it or a gasket somewhere.
Any pic ????