Originally Posted by
Wylietunes
In this scenario, we typically find that the air is a result of air trapped in the fill plumbing, when the boat is launched. IMO, check valves would likely not help. With aerator fill pumps, Some check valve designs and their location in the fill line, can actually cause the fill pump to air lock, by trapping air below it, not allowing the incoming water through the pump.
Vent line is the best resolution. If these are actual Fly High brand Fatsacs(R) then they should have 2 fittings on the top.