If there was a winepress that contained pressed grapes that became cracked and was repaired by a gentile, if the cracks were internal, the wine is prohibited - some wine would have filled the crack and been touched by the gentile and if it then ran down into the vat, it would prohibit the entire collection of wine there. If the cracks were external, it is permitted.

(Rav Huna citing Rav): Wine flowing into the vat is like the vat. (This is assumed to mean that all of the wine is connected to the wine in the vat through the stream and it also becomes Yayin Nesech).

Question (R. Zeira): In other cases (of impurity), a stream does not create a connection; so why here does it create a connection?

Answer: Rav Huna reasons that a stream creates a connection - if the gentile touched the wine in the vat, even the wine in the stream becomes prohibited (as that wine will then flow into the vat); but if he touched the stream, the wine in the vat remains permitted (as we do not view the wine in the vat as if it rose upwards).

R. Ba does not say that Rav Huna reasons that a stream creates a connection for Yayin Nesech. Rather, if the wine in the vat became Nesech, the stream is not prohibited and vice-versa. When Rav Huna said in the name of Rav that the stream is like the vat, it merely means that just as the wine in the vat can become Nesech, so can the stream.

(In Bavel in the name of Rav): If a gentile touched the stream, the wine in the vat becomes Nesech.

(Rav Nachman bar Yaakov): Only when the stream was already connected to the vat.

An Aramean gentile fell into a vat of wine. The case came before Rav Huna who ruled that they should grab his hands to prevent him from shaking them in the wine (which would make it prohibited) until they drain out the wine.

Question (R. Chaninah): But he stretched out his arm (so why are you not concerned that he shook it)?

Answer (Rav Huna): Bring baskets and take out the wine that is under his arm (to prevent it mixing with the rest of the wine).