B737 Fuel leak
On the B737NG, a checklist is published for an inflight engine fuel leak.
How can one be sure that the leak is in the engine, and not the fuel tank?
I reckon that the best thing to do is to follow this checklist (also on the B737-EFIS, where this checklist is not published). If the fuel continues to dissappear, you will have a leak in the tank, and you could restart the engine you did shut down, and use the remaining fuel in the leaking tank, and eventuelly a crossfeed from the good tank.
Any other ideas on how to check where the leak is?
On the BAe146 we had a complete troubleshooting for fuel leaks. In the event of a leak in the fuel line towards the engine, we could let the engine run on its own fuel suction. This way the fuel lines were not under pression, so the fuel would not leak, instead because of the suction from the mechanical engine fuel pumps, you would suck the fuel from the engine, like a gravity feed, and additional where the leak is, some air would be sucked in as well. The engine would mosty probably not perform at high regimes, but an idle regime would be sufficient, and it would allow you to keep the engine GEN and/or the engine driven hydraulic pump.
Since this is an item boeing does not seem to cover, I expect 10 different companies to have 10 different procedures..