Commento su Miqwa'ot 9:7

זפתין (pitch/asphalt workers) – those who apply pitch to barrels. Alternatively, those who make the pitch/asphalt.

They do not block in the case of aprons belonging to workers in pitch, potters, or trimmers of trees. Rabbi Judah says: the same applies also to summer fruit-driers. Since these people don't care how dirty their aprons become, stains never block successful immersion.

מפסלי אילנות (trimmers of trees) – that take the refuse from the trees. Another explanation: Those who cut down the trees. The language of (Exodus 34:1): “Carve [for yourself] (two tablets of stone like the first),” that he cuts the branches from the tree in order that it should become thick and that the body of the tree will grow.

This is the general rule: if it is something which one cares enough [to remove], it blocks; but if it is something which one does not care enough [to remove], it does not block. This is the general rule that basically explains the entire chapter. If the person is assumed to want to remove the stain from his clothing, vessel or himself, then it does block immersion. But if he doesn't care that it's there, then the person or article/vessel can be immersed even with the substance on it.

של קייצין – who spread them out in the sun to dry out the fruit of the summer. Another explanation: those who collect the summer fruit. But all of these are not mindful regarding the dirtiness of their aprons. But the Halakha is not according to Rabbi Yehuda.