You're not allowed to benefit in any way from Yayin Nesach (libation wine), including from the money somebody would receive for selling it. He will talk about a Jewish worker who was working for a non-Jew, and the non-Jew wanted to pay him in wine, in Yayin Nesach. The Mishnah says that the idol worshiper who hired the workers wanted to pay them with a barrel of Yayin Nesach. The Jewish workers are allowed to tell him, “Give me the value of the wine you were going to give me in money instead. Give me the cash value.” You're allowed to say that because the employer actually owes you money, not wine. So when you say that to him, it's not as if you're trading wine back to him for Yayin Nesach, which would be a problem. You're simply refusing to accept Yayin Nesach as payment and asking for cash instead. But if the Yayin Nesach has already entered your possession and you legally acquired it, at that point you wouldn't be able to trade it for cash. Once you accept the wine as payment, it's owned by you, and therefore, if you trade it for money, that would basically be selling Yayin Nesach. That would be Asur (forbidden), because you're benefiting from Yayin Nesach.
We'll continue to talk about the rule for selling wine to an idol worshiper. Once an idol worshiper touches the actual wine, it becomes forbidden. But it's not only touching the actual wine: even shaking the container a little bit would also make the wine Yayin Nesach. So, in order to avoid benefiting from Yayin Nesach, the Jew has to sell the wine before the Goy (non-Jew) turns it into Yayin Nesach.
The Mishnah says that if a Jew sells wine to an idol worshiper and wants to benefit from it—obviously, he wants to take that money, use it, and benefit from it—then if he sets the price before measuring out how much the non-Jew is going to buy, and the idol worshiper agrees to it, the Jew then puts that amount of wine into a container, and the idol worshiper takes it. Damav Mutarin, the money is permitted for the Jew to benefit from. The moment the idol worshiper grabs the container, even before he shakes it or lifts it toward himself in a big way, that millisecond, or that millimeter, that he moves it, it has now been acquired by the idol worshiper before it becomes Yayin Nesach. It's just regular Jewish-owned wine at that point. Once the non-Jew grabs it and shakes it a little bit, that's when it becomes Yayin Nesach. So, if the price was set and everything was agreed upon before he took the wine, then the moment he took the wine, he did Kinyan Meshichah (acquisition by pulling). Even before the Halacha (Jewish law) that makes it Yayin Nesach kicks in, the Jew was allowed to benefit from that wine.
But if the Jew measured out the wine and then gave it to the idol worshiper before setting the price, and the idol worshiper accepted it, and the price was set afterwards, then Damav Asurin, the money would be forbidden. The idol worshiper hadn't made up his mind whether he wanted to buy the wine when he took the container, because maybe it was going to be too expensive for him. So, when he took possession of the wine in his hand, literally, he never really acquired it. Therefore, when he touched the wine in the container or shook it a little bit, it became Yayin Nesach, but the Jew still owned it at that time. Therefore, if the sale kicked in afterwards, when they agreed on the price and wanted to make the sale, the wine was already Yayin Nesach when it was being sold. The Jew was not allowed to benefit from that money, because he would be benefiting from the sale of Yayin Nesach.
Next case: Hanotel mashpech u'madad letoch tzluchito shel Oved Kochavim. The Jew took a funnel, put it into the idol worshiper's bottle, and poured wine into it. There was already Yayin Nesach in that bottle. V'chazar u'madad letoch tzluchito shel Yisrael. Then he took out that funnel, the same funnel, and measured wine into the Jew's bottle. im yesh bo akevat yayin asur. If the bottom of the funnel had a little bit of a wine retainer, that means that some wine would be poured down, but while the funnel was being pulled out, not all the wine that was in the tube would go into the bottle. Some of it would come back out with the funnel. That's a retainer: those last drops would stay in the funnel. Then we say the wine that was afterwards poured into the Jew's bottle is prohibited.
The reason is that we have an idea called nitzok chibur. The flow of liquid that's happening connects it to the liquid on the bottom to the top. So here, in this case, the yayin nesach that was already in the bottle is connected to the funnel. Now, when you have wine being poured into that funnel, there's a chibur (connection) created. All the wine that's in the funnel turns into yayin nesach the moment it enters the funnel, because it's connected in one stream to the wine at the bottom of the bottle. So when the funnel is pulled out and there are still some drops of yayin nesach in there, or still some drops of wine in there, that wine is considered to be yayin nesach because at one point it was physically connected to the yayin nesach at the bottom. It's a chibur. Therefore, when it went into the Jew's bottle afterwards, it was yayin nesach. And even if it was just a tiny bit of yayin nesach, it prohibits whatever became mixed in with it.
The opposite case: If a Jew has kosher wine in one container, and there's another container with yayin nesach, and he pours the kosher wine into the yayin nesach, but the stream of wine is interrupted as he does this—he's throwing a little bit in—then whatever wine leaves the bottle is out of the bottle. It's not connected to the wine in the kosher bottle he's pouring from. Then it lands in the yayin nesach. We say the wine in the first bottle, the one that was kosher, the container he poured from, is permitted, because it doesn't create a chibur. It doesn't create a nitzok chibur: an interrupted flow of liquid from the problematic container of yayin nesach to the kosher bottle of wine. There's an interruption between them because he's not pouring it, let's say, right there and holding it up. It's just a short spurt of kosher wine as he's putting it out there. So there's no uninterrupted chibur. But the wine into which he poured it is prohibited because there was already yayin nesach in there. Even though he's pouring kosher wine into it, the kosher wine becomes part of the yayin nesach, and that becomes problematic.