Remove the feed line at the fuel tank, using a low pressure line such as an air line set to around 5-10psi, pressurise the feed line with it full of fuel. Clamp the line as near to the fuel filter as possible, you will see fuel leaking from the line underneath. Paint the line with a soap solution, usually i part washing up liquid to two parts water, id bubbles form you have your leak, and can sing "i'me forever blowing bubbles".