New meshing with GAMBIT
 

Hi,
I'm new using GAMBIT meshing and I'm having some dificulties.

I'm trying to mesh a porous disc, to create a pressure jump, inside a water tank considering a water-air interface.

1. I create the geometry of the disc as a face and the tank as a volume. Is this correct or I should create the disc as a volume?
2. I mesh the disc.
3. Delete the volume of the tank, leaving the faces behind.
   
4. And when I try to create a unique volume, selecting all the faces, gives an ERROR displaying: Unable to create volume because face "disc" is not utuche to the volume.
   

How I can attach the face "disc" into the volume?

Any help will be appreciated.
Regards,
Eduardo