im making a gas tank . can some one give me the low down on sealing and pressure testing the tank . my welds are (seam to be) good but i dont want to paint it and find a leak . the tank is a fat bob style and it has a 4inch by 6inch opening in the top for the sending unit .so how the hell do you seal that off to pressure test it. also is there a better product than the kreem combo pack that j&p sells in there catalog.