The headword adverb, first attested in Archilochus, often implies stooping forwards to engage in (or be subject to) a sexual act, in this instance buggery.
[1] Aristophanes, Knights 365 (web address 1), with comments from the scholia. For e)celw= ('I will drive out'), which occurs here and in most mss of Aristophanes, most modern editors accept Porson's emendation to e)ce/lcw ('I will drag out'). Most also prefer the reading of the genitive (used in a partitive sense) th=s pugh=s, which occurs in some mss, to the dative found here, th=| pugh=| ('by/with the arse'). Both produce little substantial difference in translation.