What you are after is an air seperator most fuel pumps have them fitted. basically it is a cylinder with a float inside an inlet pipe and vent at the top and drain line back to pump if no fluid is present the air goes to atmosphere when the pump expells the air the cylinder fills with product till the float seats a valve at the bottom of the cylinder.Gilbarco wayne pumps etc should have them. You just need to remember to earth everything if retrofitting to an existing pump.