after you shut the car off. First pressurize the system. Pinch the return line then immediatly pinch the sending line between the your fuel gauge and fuel filter so the gauge is inside the loop you just clamped off. Now the pressure should hold longer than your previous test of 2 hours. If not then its leaking in the motor. To pinch the hoses off I used vise grips with two pieces of metal in between them and the hose to protect the hose. Fuel dampers and fuel pressure regulators sometimes leak through the vacuum hose into the intake manifold, but while pressurized you can take the vacuum hoses off and look to see if there is gas in either of them to elliminate that. If all that holds up you can then take one vise grip off at a time to determine exactly where the fuel is bleeding off. Hope this helps. Good luck
