Okay good people - here's the reveal, probably be something of an anti-climax, but hey-ho.
Think ChrisR has spotted the tell-tale sign... The wine glass is real, has blackcurrant squash in it, I cut a disc slightly larger than the top of the glass from a orange juice carton (waterproof, stiff, flat, thin), and put that on top of the glass. Then placed a piece of wood on that, and tipped it upside down, a small bit of leakage but the paper disc stays, sealing in the liquid.
Then, to the bathroom, suspended the upside down glass in the bath with a piece of wood and thread, and shot from one end to the other. Lit the curved part of the bath with two small LED kids lamps. Had to use the tilting screen and liveview to frame the shot.
Shot with camera tipped, as seen here. (straightened).
The liquid did leak, I tried to blot it up as best as I could, but some escaped which is what gave rise to the reflected part ChrisR spotted.
I also took a shot of the empty wine glass in the same position, to give the highlighted rim, which I blended in. And shadow added under the glass in PP too.