Commentary for Avodah Zarah 142:7

Again, we reject the previous conclusion. The purchaser does acquire the wine as soon as it is put into his jug. And still the wine becomes nesekh before it hits the bottom because there might be a little bit of wine belonging to the non-Jew left over in the vessel into which the Jew pours his wine. As soon as the Jew’s wine hits this wine, it becomes nesekh, even before it is acquired by the non-Jew.

Rav’s instruction seemingly do not accord with Rabban Shimon b. Gamaliel. Rabban Shimon b. Gamaliel says that when yayin nesekh (in this case, the drop in the vessel) becomes mixed up with non-nesekh wine (the Jew’s wine), the entire mixture can be sold to a non-Jew minus the value of the nesekh. So why should he not be able to receive payment for his wine when it became nesekh in the possession of a non-Jew?