Leaking Fuel Tank

  I would suggest removing all the trim around the tanks so you have full access to the tanks and fuel lines, drain the tanks and lines, then pressurize the wing tank system with low pressure air (mouth pressure is enough), then brush all the joints and seams with soapy water and watch for bubbles. This photo is of me testing my fuel tank for leaks. The rubber glove (I didn't have a balloon) acts as a pressure regulator so I don't over pressurize.