Free form surface in fluent, two ways?
 

I am trying to model the flow in a tank and want to specify the free form liquid at the top of the tank. I tried some searching on this forum and came up with two results.

1. Define the surface as a wall and then put the Shear stresses to 0 for x and y.

2. Define the surface with symmetry boundary condition.

Can you please suggest which is better approach, as for 2, is it correct for setting the surface as boundary because i thought that symmetry meant just a 'mirror' in fluent.

Thanks