Reference for Tahorot 9:3
נִגְמְרָה מְלַאכְתָּן, הֲרֵי אֵלּוּ מֻכְשָׁרִין. נָפְלוּ עֲלֵיהֶן מַשְׁקִין, טְמֵאִין. הַמֹּחַל הַיּוֹצֵא מֵהֶן, רַבִּי אֱלִיעֶזֶר מְטַהֵר, וַחֲכָמִים מְטַמְּאִין. אָמַר רַבִּי שִׁמְעוֹן, לֹא נֶחְלְקוּ עַל הַמֹּחַל הַיּוֹצֵא מִן הַזֵּיתִים, שֶׁהוּא טָהוֹר. וְעַל מַה נֶּחְלְקוּ. עַל הַיּוֹצֵא מִן הַבּוֹר, שֶׁרַבִּי אֱלִיעֶזֶר מְטַהֵר, וַחֲכָמִים מְטַמְּאִין:
Once their work is finished they are thereby primed [for impurity]. If [impure] liquids fell on them, they are impure, and the sap that emerges from them, Rabbi Eliezer declares pure, and the Sages declare impure. Rabbi Shimon says: They do not differ regarding the sap that emerges from the olives, that it is pure. And regarding what do they differ? Regarding that [sap] which comes out of the vat [after the oil has been removed], which Rabbi Eliezer declares pure, and the Sages declare impure.