The Greek idiom of the headword phrase is difficult to translate. Literally, κακὰ κακῶν meaning "evil things of evil things". The effect seems to be one of intensification, eg. English: "wonder of wonders".
[1] Diocles fr.2 Kock; cf. however delta 1155, which suggests that the title of this play was plural Bacchae (rather than singular Baccha as here).
[2] For πλύνω in this sort of sense see LSJ s.v., II (citing the present instance among others): web address 1 below. However, the line could also read "He will give you..." depending on where the word divisions are placed (i.e. third person singular πλυνεῖ τε for second person plural πλυνεῖτε ).