Is there a cutout in the floor directly above the valves? Maybe a pic would help. Mine can be accessed NEXT TO the tank through a removable closet floor....albeit not easily. The low point drains do not go to the tank, but rather hot and cold water lines, or terminations next to the tank.
I don't know how your floorplan is laid out, but scrounge around inside the unit for floor access.
"If the women don't find you handsome, they should at least find you handy." - Red Green