פירוש על עבודה זרה 66:9

When it is first used, the cup will absorb more of the taste of the wine placed in it. That is why there is a tendency here to agree that if the first usage, or maybe even the second usage, was with forbidden wine, the it is prohibited. But if a Jew uses it the first time, or the first two times, then the cup will absorb the permitted wine. Upon further use it will no longer absorb and therefore it is permitted.