It will depend on the type of degassing head. Some types have a spring loaded valve that passes gas and or a small amout of solution etc each time the pump pulses , so it should be able to lift solution out of the tank even when not flooded. If you always have a flooded suction a simple tee and vent stack in the suction line is the easiest way to degas.

The antisyphon valves contributes to the problems that gassing causes because without them the gas can easily pass through the pump and along the discharge pipe. Now that you have to get to 25psi push the valve open the pump basically vapour locks and stops pumping. However to get accurate dosing you should have the valves fitted.

Regards

TerryF