There's no such thing as having or not having a stab tank per se, the stab is the tank just like the wings are. During manufacture the basic stab just doesn't get the full treatment to make it qualify as a tank, and a BCF just has as much of the equipment that makes it function as a tank removed.
The classic on the other hand had flight control cables running through the structure of the stab therefore requiring the -400 to have a redesigned flight control system relocating the cables to the outside thereby allowing the stabilizer to be sealed and function as a tank.
Last edited by SMOC; 3rd Jun 2014 at 04:49.