The way I model my glasses is as follows.

I lathe the outline of the glass itself, at this point the glass has outer and inner walls.

 I then select the inside polygons that will be the liquid, I "cut" them and assign them the liquid surface, even though they still occupy the same place they are no longer physically joined to the glass itself they are a separate entity. Where the liquid will be the glass no longer has inside walls polygons,they have been cut out and have become the liquid. At no time will glass and liquid polygons occupy the same space in the final model so there is no scaling of the liquid necessary.

Once I have established my liquid polygons, I select the uppermost points of these polygons and start extruding them inwards to create the top of the liquid, merging all the points into one in the center. I now have a complete liquid model that fits the wine glass exactly. The polygons of the inside lip of the glass remain as per the above sketch that mbin was kind enough to find in the old thread.

To resume all this you have a  wine glass which has no polygons where liquid and glass would normally meet

Polygons for the glass and liquid must have their normals pointing in the directions in the sketch.

This is the way that works for me, it's a pretty easy modeling job that most modeling apps are perfectly capable or performing.

Dominique Digital Cats Media