Air in DAVCO

[Chamberpains]

Davco states on their website that champagne size bubbles are fine. it's from the turbulence in the tank from the fuel returning and being sucked right back through.

Anything bigger than champagne size bubbles and I would personally give it a good thorough look over. Including the drain valve on the bottom, reseal the pipe threads for the inlet and outlet, replace all the o-rings, and check the anti drain back ball in the inlet line. For a couple hundred bucks you can put a whole new unit on it if it's old and needs replaced.