Gemara

60b: A Nochri was found in a Gas (winepress. The wine had been removed). Rav Ashi ruled that if the Gas is Tofe'ach Lehatfi'ach (can enable what touches it to wet something else), it must be rinsed and dried. If the Gas is only Tofe'ach (wet enough to wet something that touches it), it suffices to rinse it.

72a (Mishnah): If a Yisrael used a funnel to measure wine into a Nochri's flask, and then measured into a Yisrael's, if there is a place for a drop of wine to get caught and remain in the funnel, the wine in the Yisrael's flask is Asur;

If one pours from one Keli into another, the wine left in the top Keli is permitted, and that in the bottom Keli is forbidden.

(Mishnah): Nitzok (a liquid falling through the air), Ketarfes (flowing down an incline), or Tofe'ach is not considered Chibur (connected) to be Metamei (e.g. if the bottom is Tamei and the top is Tahor) or Metaher (to join to make a Mikveh). Ashboren (a collection of water) is Chibur for both of these.

(Rav Huna): Nitzok, Ketarfes and Tofe'ach are Chibur regarding Yayin Nesech (it is as if the wine below touched the top liquid).

Objection (Rav Nachman): Do you infer from the Mishnah that these are not Chibur for Tum'ah and Taharah, but they are for Yayin Nesech? The Seifa says that Ashboren is Chibur for Tum'ah. Will you infer that it is not Chibur for Yayin Nesech?! Rather, you cannot infer your law from the Mishnah.

Support (for Rav Huna - Mishnah): If a Yisrael took a funnel... if there is a place for a drop to remain..., the wine in the Yisrael's flask is forbidden.

Suggestion: The drop is forbidden due to Nitzok.

Rejection: R. Chiya taught a Beraisa that says that the case is that the wine in the flask reached the bottom of the funnel.

Inference: The Beraisa says so because Nitzok Eino Chibur!

Rejection: No. The Tana knew that if the wine reached the bottom of the funnel, this forbids the residue. He was unsure whether Nitzok Chibur.

Support (for Rav Huna - Mishnah): If one pours from one Keli into another, the wine left in the top Keli is permitted.

Inference: The wine in midair is forbidden, because Nitzok connects it (to Yayin Nesech in the bottom Keli).

Question: If so, also the wine in the top Keli should be forbidden!

Answer: The case is, he interrupted the flow (so there was never a stream connecting the two Kelim).

Question (Seifa): The bottom Keli is forbidden.

Inference: The wine in midair is permitted, i.e. Nitzok is not Chibur!

Conclusion: The inferences contradict one another. We cannot determine which is correct. The Mishnah neither supports nor refutes Rav Huna.

Support (for Rav Huna - Beraisa): If one pours a barrel of wine into a pit (of wine), all the wine outside the barrel (i.e. the wine in midair) is forbidden.

Rejection (Rav Sheshes): The case is, a Nochri pours. A Nochri's Ko'ach (he moves wine without touching it) is forbidden mid'Rabanan. Chachamim decreed only about the wine that left the barrel.

Rav Chisda (to wine sellers): When you pour into a Nochri's Keli, interrupt the flow, or throw from afar (lest a stream connect the Kelim).

Rishonim

Rif: Rav Huna taught that Nitzok Chibur regarding Yayin Nesech.

Ran (34a DH Asur): The drop of wine left in the funnel is forbidden according to the opinion that Nitzok Chibur. It is as if it is connected to the Nochri's wine below. The Yerushalmi's text says Akeves with a Kuf, i.e. dirt. Surely one may not drink the wine even if no drop remained, for one needed to rinse the funnel. We forbid Hana'ah only if a drop remained. If not, it is no worse than Kelim of Nochrim, which forbid drinking, but not Hana'ah. Sincewe hold like R. Shimon ben Gamliel who permits selling a mixture of Stam wine except for the Isur, why do we forbid Hana'ah due to Nitzok? Why does the Rif forbid? Perhaps even R. Shimon's law is only when he specifies (that he sells only the Heter), but a Stam sale is forbidden, even if he will not benefit from the Isur. Others say that 'Asur' means to drink. When no drop remains, one may even drink it. Even though the funnel was not rinsed, since wine is not stoed in it, if the wine dried, it does not forbid wine put in it. The Ramban says so only for a funnel, since wine does not remain in it, but not for cups and similar Kelim.

Rambam (Hilchos Ma'achalos Asuros 12:12): If one pours wine into a Keli with wine of Nochrim, all the wine in the top Keli is forbidden, for Nitzok connects the top and bottom Kelim. Therefore, one who measures out to a Nochri holding a Keli should interrupt the flow, or throw it, lest a Chibur of Nitzok forbid the top Keli.

Ra'avad: I say that one may not drink the top wine.

Rosh (5:26): R. Tam says that Rav Huna did not teach his law on its own. Rather, he derived from the Mishnah that Nitzok, Ketarfes and Tofe'ach are not Chibur for Tum'ah and Taharah, but they are for Yayin Nesech. The text was emended to say only Nitzok, for our entire Sugya discusses only Nitzok. The conclusion is that Nitzok Eino Chibur. Rav Huna did not have a reasoning or tradition that it is Chibur. He merely inferred from the Mishnah. Rav Nachman refuted this, so Rav Huna retracted. On 60b we require Tofe'ach Lehatfi'ach. Since his Diyuk is not true regarding Tofe'ach, also it is not true regarding Nitzok. We inferred from R. Chiya's Beraisa that Nitzok Eino Chibur. The rejection was flimsy. Also, Rav Sheshes answered that the case is that a Nochri was pouring. We rely on this to permit a Nochri's Ko'ach for what did not flow outside. Rav Chisda told vendors to interrupt the flow. This was not due to Nitzok Chibur. The Gemara did not infer that Nitzok Chibur, and it put teachings about Ko'ach between his and the teachings about Nitzok Chibur. Rather, his teaching is due to Ko'ach. The vendors poured into Kelim of Yisrael, and from them to Nochri Kelim. Sometimes the Nochrim help, and the vendor is unaware.

Poskim

Shulchan Aruch (YD 126:5): If one pours wine into a Nochri's Keli that was not rinsed and does not have liquid Tofe'ach, one may not drink the wine in the bottom Keli, but one may drink the wine in the top Keli.

Tur: Some say that even Nitzok of Stam wine of Nochrim forbids Hana'ah. The Rashba says in the name of Ge'onim that Nitzok Chibur only when pouring into real Yayin Nesech, but not when pouring into a Nochri's Keli that was not rinsed.

Beis Yosef (DH Yesh): Why did the Tur cite the Rashba's first words about Yayin Nesech, and conclude with a Keli that was not rinsed? He should have taught about Stam wine of Nochrim! It is not clear from the Tur what the law is. The Rashba explicitly permits benefit from it, but not if one poured into Yayin Nesech, as if it mixed. He says that some forbid every Nitzok, but he disagrees. He cites Ge'onim that Nitzok Chibur only when pouring into wine Asur b'Hana'ah. Therefore, when one poured into a Nochri's Keli, even if it was not rinsed, one may not drink the wine in the bottom Keli, but one may drink the wine in the top Keli. It seems that he permits only when there was no wine in the Nochri's Keli, for then it would be forbidden to drink the top wine. Pouring into a little wine is like pouring into much wine. The Ge'onim said that Nitzok Chibur only for Yayin Nesech, but not for Stam wine of Nochrim. It seems that that even Tofe'ach that is not Lehatfi'ach forbids Nitzok. Rashi explains Rav Huna this way. However, R. Yerucham forbids only if it is Tofe'ach Lehatfi'ach. The Semag and Tosfos (6ob DH Iy) agree. However, R. Yerucham agrees about a Keli in which wine is normally stored that it need not be Tofe'ach Lehatfi'ach.

Taz (6): The Tur holds that one opinion (the Ra'avad) forbids Hana'ah due to Nitzok of Stam Yeinam (wine of Nochrim). We give the stringency of the bottom to the top. It is not because we consider them to be mixed, for really, they are not mixed. The Rashba disagrees, and says that the stringency is to consider hem to be mixed, so it is Batel in 60. The Rashba holds that Nitzok Chibur only for intact wine, be it Yayin Nesech (which forbids all Hana'ah) or Stam wine (in which case one may sell the rest of the wine). If one poured onto a Keli that was not rinsed, it merely has absorbed Yayin Nesech, so one may drink the top wine. The Rashba says 'full Yayin Nesech', but this includes Stam Yeinam, for later he is lenient about Kelim of Nochrim (since they merely absorbed Stam Yeinam). The Tur argues with both of these. Just like Chachamim required 60 parts of Heter to Mevatel Isur absorbed in a Keli, as if the entire Keli were Isur, also here

Gra (11): The Rambam holds that Nitzok Chibur. A support is 71b (we challenged only the opinion that Nitzok Eino Chibur).

Rema: If there is Tofe'ach Lehatfi'ach, Nitzok forbids. However, it does not forbid more than if mixed with it. Stam wine of Nochrim is Batel in 60.

Shach (10): If wine is stored in the Keli, it forbids even if there is only liquid Tofe'ach.