Your final solid (volume) has to represent the airflow path, so somehow your inner and outer funnel airflow paths have to form a single volume. For more try "Overview: Geometry To Results"

A watertight volume will have each edge shared by 2 faces - so if you think there's a problem area try selecting an edge and checking that it also shows 2 faces and a single volume in the selection dialog.

The Fix tool under 'Others' on the Geometry Tool Palette can stitch faces into a volume if their edges are within a tolerance. If it fails then there is likely a problem with the geometry - usually an opening or an edge shared by more than 2 faces (non-manifold geometry).

If the fix tool reports no problems then a final check would be to create a volume grid by adding a Substance (e.g., Air from Physics Tool Palette->Substances) and requesting the Position attribute (Results Tool Palette->Vector Fields) on the volume. If there's any topology problems the mesher will report an error. This is essentially producing a mesh, for more try "View a Mesh"

Note if you want to perform a Panel Flow simulation (State->Viscous = No, State->Rotational = No) you will have to ensure that the mass (or volume for incompressible flow) flow-rate (volume flow-rate = velocity * area) through the inlets matches that through the outlets. Also you shouldn't have inlets or outlets sharing a common edge - this will cause a step change in velocity (shear flow) which will cause problems for a panel method (inviscid flow).

For a RANS Flow simulation you don't have to worry about the mass balance between inlet and outlet.