The halacha is that if one pours wine that is not kosher [יין נסך] into a pit filled with wine that it kosher, the non-kosher wine is nullified and may be drunk.
When wine that was poured as a libation to idols is mixed with [other] wine, it is forbidden to benefit from the entire mixture regardless of how small [the amount of forbidden wine], as we explained.
When does the above apply? When the permitted wine is poured onto a drop of wine that had been poured as a libation. If, however, one poured wine that had been pour as a libation from a small bottle into a cistern of wine, its presence is nullified. Even if one poured the entire day, each individual drop becomes nullified, drop after drop. [Rambam Maachalos Assuros 16/28]
Some say that this applies even if there is not 60 times permitted wine. If so, how come the Jews [in the time of the Greeks] didn't take the tamei oils and pour them into the tahor cask of oil and the whole thing would be tahor and they would have PLENTY of oil?
If one wants to answer that אין מבטלין איסור לכתחילה then we will answer that for the sake of a mitzva one may be mevatel issur lichtachila [S.A. Orach Chaim 626].