Create a new layer and call it "Glass." Make a quick drawing with your Pen Tool to create one half of the glass; fill it with black and no stroke. Duplicate the shape, reflect it horizontally and snap it to the first half.
Select both shapes and unite them with the option in the Pathfinder panel. Select the glass and give it a three-step linear gradient with: K=8 at 0%, CMYK=15, 0,35,8 at 72%, and K=8 at 100%.
Make an ellipse to form the opening of the glass. Fill it with a white-to-black linear gradient, no stroke, then set it to Screen blending mode and lower the Opacity to about 55%.
You can play with the settings for awhile until you get it right for your glass. Next, draw some highlights on the same layer to better define the opening. Use a gradient as shown below to fade the highlights at the ends and leave specular highlights on a few places. So much for the glass, moving on to the fluid.
