About tetgen using

My question is about the example “cube with balloon” ( from manual ).
How can I use Tetgen to do a cube without a balloon?.
This is the problem, the streamlines don’t see an internal surface (for example balloon) as an obstacle. Despite fixing the labels and regions for boundary conditions.
My geometry (not a balloon) is very complex for use buildlayers.

Dear user
See the example
FreeFem-sources/tetgenholeregion.edp at master · FreeFem/FreeFem-sources · GitHub