They used JB Weld because the tank was leaking. That isn't the preferred way to fix a leak. I usually have the tanks re soldered. They leak around the top where the vent line and feed lines are, and they leak a bunch at the base of the filler tube. The filler tube usually leaks because pressure is put on the tube when you fill the tank. They install a reinforcement ring and solder that in. The tanks probably leaked from the factory though.
In California they test for leaking tanks and you fail the test if the tank won't hold pressure. With OBD II, there are sensors that do the test so the emissions test don't need to include that test on those vehicles.
