Fuel Tank Capacity???

the ground wire is hooked to the fuel line? looking at the sending unit under the car, i see the fuel line coming out, and just to the right of it, the stud with the blue wire...maybe its not grounded at all. I assumed it would ground with the tank...
So there should be 2 wires visible along with the fuel line on the outsideof tank?? Once again, thanks for the help folks