Avraham Sacks asks:
Ravina said we cannot purposely make a Graf Shel Re' but if we invited a Jewish guest or drank wine ourselves we would intentionally be making a Graf Shel Re'i, so what is different about the leftovers in the non Jew's cup?
Avraham Sacks, Ramat Beit Shemesh
The Kollel replies:
Dear Avraham,
There is only Graf by the leftovers of a non-Jew since the wine is forbidden to use and therefore Muktza. Jewish wine and leftovers is not Graf since it can be used by chickens.
All the best,
Reuven Weiner