פירוש על מכשירין 3:2

חבית (jar) – of earthenware or soft stone vessel that is like earthenware. But the rest of the vessels that did not observe so much until the fruit that are within them absorb.

A jar full of produce which was put into liquids, or a jar full of liquids was put into produce and [the produce] absorbed, all [the produce] which absorbed comes under the law of ‘if water be put’. The jar is made of earthenware which will easily absorb water. It doesn't matter whether the jar has liquids and it is put into the produce or the jar has produce and it is put into liquids in all of these cases the produce that has absorbed any liquid is susceptible to impurity. This is true even of pulse (mostly beans) which is less absorbent than other produce such as grain.

שאבו – the fruit became moistened and liquid was dripping on them. This is our reading.

Concerning what liquids were they speaking? Water, wine and vinegar; but all the other liquids do not cause susceptibility to uncleanness. This halakhah is limited to two of the 7 liquids that cause susceptibility: water and wine (vinegar is made of wine). The other liquids (we will see the full list in 6:4 dew, oil, blood, milk and honey are the other five) are thicker and will not be as easily absorbed. Therefore, they won't cause the produce to be susceptible.

ושאר כל המשקין טהורים – the rest of the seven liquids (see Tractate Makhshirin, Chapter 6, Mishnah 4: milk, [olive] oil, honey, blood) that make something fit to become susceptible for receiving Levitical uncleanness, the fruits are ritually pure that are within the jar if they were moistened by them. For specifically water and wine and vinegar which are thin and clear, they are absorbed in the jar because of their thinness and the fruit absorbs [liquid] from them. But [olive]oil, honey, milk and blood and dew, are thick, and because of their thickness they are not able to be absorbed within the vessel so much until the fruit that is within the jar absorbs from them. Therefore, they are not [included] in “when water is put on” (Leviticus 11:38).

Rabbi Nehemiah says pulse is insusceptible, because pulse does not absorb [liquids]. Rabbi Nehemiah says that pulse put in such a jar is not susceptible to impurity because it is less likely to absorb the liquid. In other words, whereas the previous opinion only limited the thicker, less absorbable liquids, Rabbi Nehemiah adds that the thicker less absorbent produce doesn't become susceptible to impurity.

שאין הקטנית שואבת – as for example, split beans and beans and things like them. But the Halakha is not according to Rabbi Nehemiah.