Commentary for Avodah Zarah 145:14

Such a device was evidently used at the house of the exilarch, the Jewish governor in Babylonia. It is not surprising to hear that in such a place, Jews and Gentiles would drink together. In any case, the rabbis permitted, and maybe even used, this device.

If even a drop of yen nesekh falls into a large container of permitted wine, the entire container of permitted wine is forbidden.

If forbidden wine (yen nesekh) should become mixed with permitted (as we learned in section one) or forbidden water (that was used for idolatrous purposes) should be mixed with permitted water, the entire mixture is forbidden, even if the forbidden substance was only a drop.
However, if forbidden wine should become mixed with permitted water, or forbidden water with permitted wine, as long as the forbidden substance does not impart a flavor to the mixture, the entire mixture is permitted. If the forbidden substance imparts flavor, the entire mixture is forbidden.

This section teaches a general rule from which the specific rule taught in the previous section may be extrapolated.

According to R. Dimi, when each drop falls into the vat it is annulled because it is such a small amount. Once it is annulled, it becomes part of the undifferentiated wine in the vat and then the next drop is annulled. At a certain point the majority of wine was originally yayin nesekh and has, in a sense, been made kosher.

The mishnah seems to say that even the smallest amount of yayin nesekh renders the wine it falls into prohibited. This is a clear contradiction to R. Dimi.
The Talmud answers that the mishnah refers only to when permitted wine falls into prohibited wine. But if prohibited wine falls into permitted wine, it is nullified. [This is clearly not the simple reading of the mishnah].

The Talmud now proceeds with the next line of the mishnah—when wine falls into water. It seems that this too is a difficulty on R. Dimi. If prohibited wine falls into water it prohibits as soon as it imparts a taste. We don’t say that each drop is nullified. The Talmud again adjusts the mishnah—the wine is permitted and it falls into prohibited water. Prohibited water is water that was worshipped. [Again, you can sense that we are straying from the simple meaning of the mishnah].

Now we move onto the last clause. If the mishnah is dealing with prohibited water, then in the last clause, to maintain consistency, the water should again be prohibited. This is certainly a difficulty on R. Dimi. We do not say that each drop of prohibited substance is annulled.

R. Dimi says that the whole mishnah deals with permitted substances falling into prohibited substances. That is the consistency in the mishnah. But whether the water is permitted or prohibited changes from one clause to the next. What is crucial is that to R. Dimi, when a prohibited wine falls into permitted wine, the permitted wine nullifies the prohibited wine. This is a giant leniency in the laws of forbidden mixtures.

This is a slightly more limited version of R. Dimi’s statement from yesterday’s section. If one pours yayin nesekh from a small vessel into a large vat, each drop is annulled. But if one pours from a large vessel, enough yayin nesekh falls in at once such that it cannot be annulled.

Rabin’s statement is a third tradition coming from R. Yohanan. To understand this we have to remember that according to the Mishnah, if yayin nesekh falls into kosher wine, the prohibited portion causes the entire mixture to be prohibited, even if it is the smallest amount. This is a case of a species becoming mixed with its own species. But if the prohibited wine falls into water, it must give taste to the water for the mixture to become prohibited. Rabin addresses a case where water and nesekh fall into a vat of wine. In such a case, we can ignore the permitted wine, and not see this is as a case of yayin nesekh falling into permitted wine. Rather, we look at it as if the nesekh fell into the water. If there is enough water to annul the taste of the small amount of nesekh (and there probably is) then the entire vat remains permitted.

If the wine falls into the vat first, then the entire vat becomes prohibited because both are the same species. Only if the water falls in first can we consider it as having annulled the wine.

In this version of R. Shmuel b. Judah’s statement, he makes his statement about the mishnah, not with regard to Rabin’s statement.

The difference between the two statements is whether the flask of water must fall in first. If it is taught about the mishnah, then R. Shmuel b. Judah just said that there must be a flask of water that falls into the vat. It can fall in there right after the yayin nesekh falls in. But if we teach it about Rabin’s statement, then R. Shmuel b. Judah must come to add that the flask of water must fall in first for the vat to remain prohibited.

According to Hizkiyah, if forbidden wine falls in first to a vat, then the entire mixture is prohibited. The fact that water falls in after will not change the fact that the entire mixture is prohibited. But if the forbidden wine and water are first mixed together, then this mixture will be permitted, assuming that the water nullifies the forbidden wine. If this entire mixture now falls into a vat of permitted wine, the entire vat remains pure.
R. Yohanan says that even in the first case, the mixture is permitted.