A large amount of gas is leaking from somewhere above the gas tank area only when car is running. Dropped tank and no visable leaks in tank or lines.
Possibly there is a feed line from the fuel pump going across that area that has a crack or is loose?
high fuel pressure runs up to engine and excess is returned to tank still high pressure , you would have to run the pump while tank is dropped ,a pinhole would be a heavy leak , dangerous job. punch hole in tank corner, drain and remove all gasoline, move away,, drop tank fill with water ,plug small punched hole with self tapping rubber washer roofing screw plug in wires have someone work key on off see the leak!
Obviously you dropped the tank already and no need to punch a hole in it. No matter how good a rubber washer for roofing is. I have lowered them down full of gas by myself, so can be done. it should not be too difficult to locate the leak, look around better, check the pump O' ring/gasket, rubber lines if it has them, or any area that looks rusty or very clean or damp, Check those fittings to the pump assembly and fuel filter if its near by. I would have a chemical fire suppressor on-hand if you decide you have to turn the ignition switch on to locate it, the few seconds to prime should be enough to locate it so I would not crank it or leave it turned on very long, have help on-hand, and near by.
If you fill the tank with water and turn ignition switch to the on position the water will go straight to the motor via first the fuel filter so do not do that and pressure will not pressurize the lines if you decide to try this and disconnect the fuel lines from motor so my advise is do not fill you engine with water nor punch holes in your fuel tank..
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