Going on, off and on, as a colonic goes off (10)

I believe the answer is:

occasional

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'going on' is the definition.
(thesaurus)

'as a colonic goes off' is the wordplay.
'goes off' indicates an anagram.
'as'+'a'+'colonic'='asacolonic'
'asacolonic' with letters rearranged gives 'OCCASIONAL'.

'off and on' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for occasional that I've seen before include "Happening now and again" , "Rare" , "Occurring infrequently" , "irregular" , "infrequent" .)

I've seen this clue in the Sydney Morning Herald.

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