One source of air bubbles is loose connections to the degasser inlet/outlets. The end of the tubing and flat side of the ferrule should be perfectly aligned and then tightened securely.  One way to be certain of these is to tighten the fitting down very hard by hand. This will cause the ferrule to crimp onto the tubing. Then when you undo the fitting, the ferrule won't slight on the tubing.  If any tubing is extending beyond the ferrule, cut if off with a sharp, clean razor blade. Reconnect the tubing and fitting to the degasser.