first check during the filling if there is any petrol dipping on the floor, that means the metal pipe is leak and needs replacement.
Second check the over flow pipe if that has made its way into the car, its located behind the left tail light.
thirdly check the fuel pump if it is not leaking. chances are less if its genuine, and most likely if its a Chinese or Desi one...
lastly check the pipe from carby that goes back to the tank, as if it is not choked....
hope this would help....