The first step is to define three points. Then it is possible to create a cylinder between two of them with the choice 10 of the menu. The different tolerance values have to be  modified to get a best geometry.
The third point is to define fluid domain.

In our case, to be able to create meshing, it is necessary to convert initial surface (cylinder) into B-SPLINE surface.
This surface corresponds to an interpolation and approximation-boundary curves.