Commentary for Avodah Zarah 144:6

This baraita seems to imply that flow is a connective. As soon as the wine flows out of the cask into the vat of yayin nesekh, the wine becomes prohibited. R. Sheshet says that the baraita refers to a case where a non-Jew is doing the pouring. Thus he invents a new category that is not found in tannaitic sources—wine poured by a non-Jew is considered nesekh.