Gemara

56b (Rav Huna): If one emptied out the strainer that catches grape skins and peels back into the Gas (winepress), this forbids the Gas.

Inference: The strainer itself is Asur due to Nitzok (a liquid falling through the air into another liquid, i.e. the wine in the pit).

Rejection: No, the wine in the pit reached up to the strainer.

60a: The spigot came off a barrel of wine. A Nochri ran and stuck his hand there to prevent the wine from spilling out. Rav Papa forbade the wine at or above the level of the spigot is forbidden, and permitted the rest.

65a: Rav Acha brei d'Rav Ika's father would bring barrels of wine, sell it to Nochrim and pour it into their pouches.

71a - Rav (to Yisrael wine sellers): When you sell to Nochrim, take the money before you measure out the wine. If not, your wine will become Yayin Nesech while it still belongs to you. One may not take money for Yayin Nesech.

(Rav Ashi): If a Nochri acquired through Meshichah, he would acquire when it is measured, but it is not yet Yayin Nesech (until he touches it)!

Rejection: The seller pours wine into the Nochri's Keli. It becomes Yayin Nesech once it enters the Keli (and mixes with residues of Yayin Nesech).

Defense (of Rav Ashi): If a Nochri acquires through Meshichah, he would acquire once the wine enters the airspace of his Keli, but it is not Yayin Nesech until it reaches the bottom (and mixes with residues of Yayin Nesech)!

Inference: The opinion that rejected Rav Ashi's support holds that Nitzok (a liquid falling through the air) is considered connected (therefore, the entire stream of wine is Yayin Nesech, even what is above the Keli).

Rejection: The case is, the Keli rests on the ground. (Therefore, he does not acquire until he picks it up after it is full. It is already Yayin Nesech).

Question: This is unlike R. Shimon (ben Gamliel), who permits selling a mixture of Kosher wine and Yayin Nesech, but he takes money only for the (amount of) Kosher wine. (The Halachah follows R. Shimon!)

Answer: We are explaining Rav. Rav says that the Halachah follows R. Shimon only when barrels mixed, but not if the wine itself mixed.

72a (Mishnah): Nitzok, Ketarfes (flowing down an incline), or Tofe'ach (wet enough to wet what touches it) is not Chibur (connected) to be Metamei or Metaher. 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? If so, you must learn from the Seifa that Ashboren is Chibur to be Metamei or Metaher, but not for Yayin Nesech! Rather, you cannot infer your law from the Mishnah.

72b: A man was siphoning wine from a barrel with Bas Gishta (bent reeds. One sucks to start the flow, and all the wine flows out). A Nochri put his hand on the bottom, stopping the flow; Rava forbade all the wine left in the barrel.

Rav Papa: Do you forbid due to Nitzok?

Rejection: No. This is unlike regular Nitzok. All the wine would have flowed out of the reeds, so they are like an extension of the barrel.

(Mar Zutra brei d'Rav Nachman): One may drink from Kenishkenin (a Keli with pipes exuding for people to drink from it) at the same time as a Nochri.

Rabah bar Rav Huna himself drank from Kenishkenin.

73a (R. Yochanan): If one pours Yayin Nesech from a barrel into a pit of wine, even for an entire day, each bit poured in becomes Batel.

Rishonim

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

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 the Nitzok flow connects the top and bottom Kelim. Therefore, one who measures out to a Nochri holding a Keli should interrupt the flow, or throw it, so there will not be a Chibur of Nitzok to 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 have a reasoning or tradition that Nitzok Chibur. He inferred from the Mishnah. Rav Nachman refuted this, so Rav Huna retracted. A proof is that on 56b, the Gemara inferred from Rav Huna that Nitzok Chibur (and rejected this). Why did it need to say this? Rav Huna explicitly said that Nitzok Chibur! Rather, this shows that he retracted. In many places the Gemara asks in astonishment 'may we infer that Nitzok Chibur?!' The Gemara could have derived from Rav Acha brei d'Rav Ika's father that Nitzok Eino Chibur. It did not do so, for this is not surpising. Also, in the case of Bas Gishta, later Amora'im thought that Rava forbids Nitzok Chibur, and they were astounded. Rav Nachman's son is Basra, and he permitted Kenishkin, and Rabah bar Rav Huna himself drank from it. Do not say that Nitzok Chibur only when the flow will mix in below, but not if one sucks wine from above, for also Bas Gishta is through sucking. R. Yochanan taught that if one pours Yayin Nesech into wine, each bit poured in becomes Batel. We do not forbid the bottom due to Nitzok with the flow. This does not proof that Nitzok Eino Chibur, for Nitzok is no more stringent than if it were mixed, and if it were mixed, it would be Batel. These are clear proofs. However, Rashi, the Ge'onim and the Rif ruled that Nitzok Chibur. Rabbeinu Meir followed the Gedolim of France and he permitted Nitzok to avoid a big loss, but not for a small loss.

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.

Beis Yosef (ibid.): The Tur says that Nitzok is as if the wine is mixed, therefore, if the bottom Keli was not rinsed, one may not drink the wine, but one may benefit from it. I do not understand. The Rashba already said that Nitzok Chibur when the bottom wine is Asur b'Hana'ah! If the Tur disagrees, and holds that anything one may not drink is called Yayin Nesech, he should have brought the Rashba's opinion, and added to it! The Tur connotes that the Rashba forbids Nitzok, but not because it is as if it is connected. This cannot be. The Gemara says 'Nitzok Chibur'! The Tur says that for Stam wine of Nochrim, one should throw the Hana'ah to the sea or sell all the wine except for the Yayin Nesech. This applies only to a mixture. When we forbid the top Keli, it is because it is as if it is connected, but there is no Hana'ah from the bottom wine! Rather, one may sell all of it to Nochrim, like the Rashba said.

Taz (6): The Tur brought from the Rashba that if a barrel has wine and some water mixed in, and it fell onto a Nochri's Keli, if there is 60 times as much water as the amount of Yayin Nesech in the Keli, it is permitted. The Shulchan Aruch (Sa'if 6) rules like this. Why didn't the Beis Yosef ask here how there is Bitul, for there is no mixture? Rather, Chachamim made Nitzok like Heter that absorbed Isur due to boiling. We require 60 times as much Heter. Likewise, regarding Nitzok we require 60 times as much as the (Isur connected to the) flow. If there is less than 60, it is as if some of the Heter above became Isur, and one must throw it to the sea. The Darchei Moshe brings from the Mordechai that it is as if it is mixed. I answered all the Beis Yosef's questions against the Tur.

Shach (9): Nitzok Chibur applies only to wine Asur b'Hana'ah. Even though nowadays we permit Hana'ah from Stam Yeinam and what Nochrim touch, surely Nitzok Chibur, for letter of the law it should be Asur b'Hana'ah.

Gra (10): Terumas ha'Deshen brings from the Ge'onim that Nitzok Chibur applies only to wine Asur b'Hana'ah. This is why Rashi (72b DH Ela) forbids due to wine in the Nochri's Keli, and not due to the Keli itself. However, the Mishnah connotes otherwise. It specified 'if a drop remained in the funnel', but it did not specify that there was wine in the Nochri's Keli! This requires investigation.

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

Beis Yosef (DH u'Mah she'Chosav ha'Rashba): In Toras ha'Bayis, the Rashba says that the Ra'avad forbids Hana'ah from what is inside due to Nitzok. The Rashba argues, for we are not so stringent about Nitzok to forbid it like Yayin Nesech. It is not worse than a mixture with Stam wine of Nochrim! The Ra'avad himself explained that Rav Papa (60a) forbids Hana'ah only from what is above the spigot! What is below is no less than Nitzok! It seems that 71a supports him. Rav said 'if not, you receive money for Yayin Nesech.' However, perhaps the Gemara suggested that this shows that Nitzok Chibur and it is Asur b'Hana'ah, and later rejected the proof for both of these. We can say similarly about the episode with Bas Gishta. Alternatively, Rav is stringent because he holds that R. Shimon permits Hana'ah only when barrels mixed, but not when the wine itself mixed. Also we forbid Hana'ah when there is Nitzok to Vadai Yayin Nesech!

Beis Yosef (DH Kasav Rabbeinu): R. Yerucham says that if a Nochri touched a falling flow of wine, all is Asur b'Hana'ah, as if he touched all of it. I do not know what his source is.