Avodah Zarah 71B

מדמשכה גוי קנייה, יין נסך לא הוי עד דנגע ביה!

from the moment that he pulled it, the non-Jew acquired it, whereas it did not become wine used for a libation until he touched it. Therefore, the seller can receive payment for the wine he sold, because at the time of the acquisition the wine was permitted.

אי דקא כייל ורמי למנא דישראל, הכי נמי. לא צריכא דקא כייל ורמי למנא דגוי.

The Talmud rejects this proof: If it is a case where the seller measures the wine and pours it into the vessel of a Jew, it is indeed permitted to do so without receiving payment first. Rav’s ruling is not necessary except in a case where he measures the wine and pours it into the vessel of the non-Jew, which contains wine used for a libation, and the wine is rendered forbidden upon contact with the vessel even before the non-Jew acquires it by pulling it.

סוף סוף, כי מטא לאוירא דמנא קנייה, יין נסך לא הוי עד דמטי לארעיתיה דמנא, שמע מינה נצוק חבור?

The Talmud raises an objection: Ultimately, even in this case, when the wine reaches the interior airspace of the non-Jew’s vessel, he acquires it, as this too is a mode of acquisition. And it does not become wine used for a libation until it reaches the bottom of the vessel, making contact with it, so the acquisition occurs before the wine becomes forbidden. Can one conclude from this that in the opinion of Rav a stream of liquid serves as a connection between two bodies of liquid? If so, when the Jew pours the wine into the non-Jew’s vessel, the flow of wine that is in contact with the forbidden wine at the bottom of the vessel would render all the wine being poured into the vessel forbidden.