פירוש על עבודה זרה 5:10

שנפל לבור – [a cistern] of wine.

If yen nesekh fell into a vat, the whole of it is prohibited for use.
Rabban Shimon ben Gamaliel says: the whole of it may be sold to non-Jews with the exception of [a quantity corresponding to] the value of the yen nesekh in it.
This mishnah returns to the discussion of yen nesekh that falls into a larger quantity of permitted wine.
This mishnah contains a dispute between Rabban Shimon ben Gamaliel and the anonymous mishnah with regards to the prohibition of a mixture of yen nesekh and permitted wine. According to the first section in the mishnah it is forbidden to derive any benefit from even a mixture of yen nesekh and other wine. In essence, the wine must be thrown away. According to Rabban Shimon ben Gamaliel, the Jew may remove a quantity of wine from the mixture that corresponds to the quantity of yen nesekh which fell in, and the rest he may sell to a non-Jew. In this way he is not deriving any financial benefit from yen nesekh.

כולו אסור בהנאה – that the wine which was poured as a libation for idolatry prohibits in the same species in any [miniscule\ amount. But wine of gentiles in which it is not known if it was used for a libation to idolatry of non-Jews where they did not know about it that it had definitely been poured as definite libation, even though it is prohibited to derive benefit from it, its mixture does not prohibit deriving benefit from it, but rather, all of it should be sold to non-Jews, outside of the monies of that wine which is not known whether or not it had been poured as a libation to idolatry, and such is the Halakha.