Tosefta zu Orlah 2:18

Vessels which were oiled with unclean oil, and [later] he returned and oiled them with clean oil; Or he [first] oiled them with clean oil, and [later] he returned [to them] and oiled them with unclean oil: Rabbi Eliezer says: “I go after the first.” And the Sages say: after the last. (Orl. 2:13, Kulp tr.) To that Rabbi Eliezer says, let the person anoint his vessels with impure oil and then go back and then anoint them with pure oil, because when the oil comes out, only the first comes out (i.e., leaving the pure oil inside the vessel). And the Sages say, let the person anoint his vessels with pure oil and then go back and anoint them with impure oil, because when the oil comes out, only the last one comes out. Vessels that are anointed with impure oil, he wipes them off and can use them for [purposes of] ritual purity. [But if afterwards] he came back and [discovered that] liquid had emerged, it is impure.