The phrase 'καθαρτήν' (purifier/cleanser) functions as a substantive appositive to 'ἀλεξίκακον' (one who wards off evils), both in the accusative case governed by 'εὑρόντες'. While 'ἀλεξίκακον' is a standard epithet, 'καθαρτήν' in this specific context is a pointed political metaphor. In the play, the chorus of Wasps (old, hyper-zealous jurors) are praising the 'old man' Philocleon's ability to purge the city of 'evils' (which, in their view, are the younger generation and democratic reforms). However, the term 'καθαρός' and its derivatives often carry strong connotations of ritual purification, and here Aristophanes ironically suggests that the jury's verdicts are not just legal but a form of sacrificial cleansing of the polis, a concept that aligns with the play's broader satire of the legal system as a mechanism for social and political 'purification' through exclusion. The construction itself is syntactically straightforward, but the semantic weight of 'καθαρτήν' here is deeply ironic and specific to the play's political argument.