Outbreak: clean up? Working on it (8)
I believe the answer is:
eruption
'outbreak' is the definition.
(thesaurus)
'clean up? working on it' is the wordplay.
'clean' becomes 'pure' ('pure' can be similar in meaning to 'clean'**).
'up?' says the letters should be written in reverse (in down clue: letters go upwards).
'working' is an anagram indicator.
'pure' back-to-front is 'erup'.
'on'+'it'='onit'
'onit' anagrammed gives 'tion'.
'erup'+'tion'='ERUPTION'
(Other definitions for eruption that I've seen before include "Spot or rash appearing suddenly on the skin" , "The action of a volcano" , "Violent outbreak as by volcano" , "Breaking out (of spots, lava etc)" , "Volcanic event" .)