Commentary for Avodah Zarah 148:1

Mishnah. A vat [for wine-pressing] made of stone that a heathen [sealed with] tar: it was customary to lift a small amount of wine into it [i.e. the vat] to overcome the smell of the tar.

To scour it: [This is] explained in the gemara [as scouring using] water and ashes.

Of wood: which requires more tar since it absorbs more wine [i.e. than a stone vat]. Rabbi says scour it as with the stone [vat] and the Sages disagree.

And of earthenware, even if the tar is peeled off, it is forbidden: one might think every opinion holds this way since earthenware itself without tar absorbs wine.

There are three types of wine presses mentioned by the mishnah: stone, wood and earthenware. Stone is the least absorbent of these materials. Furthermore, stone wine presses do not require much pitch to seal them. Therefore, all the Jew must do is scour the wine press to rid it of any traces of the previous owner’s wine. If the wine press was made of wood, Rabbi [Judah Hanasi] holds that it also may be scoured. However, the Sages hold that he must also peel off all of the pitch. Since wood is more absorbent than stone, and since wood wine presses require more pitch, he must be even more diligent in cleaning before it becomes usable. If the wine press is of earthenware, the Jew may never use it. Since earthenware is very absorbent, there is no way to rid it of the yen nesekh.