'Pitch' in the sense of cover with pitch, though the other meaning of kwna/w, 'spin' is perhaps not to be excluded; see LSJ s.v. kwna/w (web address 1).
The headword phrase might be quoted from somewhere; if so, perhaps from comedy. (The Etymologicum Magnum cites Aristophanes for this aorist infinitive.)
For wine-jars (pithoi) see alpha 3230, zeta 127, pi 1585, and frequently elsewhere.