Sometimes back there was a topic under discussion on this forum regarding defining fluid density in the long vertical legs of big bore pump discharges. There is no doubt that the density in such legs should be made zero as the vertical column wt. is not seen by discharge flange. When CAESARII makes Hydrotest case on its own how does the program know this fact ? I have not checked myself and compared results of Hydro case with that of a copied model with springs replaced by +Y and fluid density put as zero in the vertical leg ( temp. ambient). But I feel the program would not know that wt. of water will not go to pump flange in hydro case.
Any suggestons?

You're right, the program won't know this.

Here is the thread you were talking about , I found it by searching on the word "vertical".