Crossword Genius

Obligation to include separate bits of toilet, not as a one-off? (5)

Ross

I believe the answer is:

twice

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'obligation to include separate' is the definition.
I can't tell whether this defines the answer.

'bits of toilet not as a one-off?' is the wordplay.
'bits of' suggests taking the first letters.
'not as' becomes 'w' (I can't justify this - if you can you should give a lot more credence to this answer).
'a one off?' becomes 'ice' (I've seen this in another clue).
The initial letter of 'toilet' is 't'.
't'+'w'+'ice'='TWICE'

Can you help me to learn more?

(Other definitions for twice that I've seen before include "Doubly" , "Two times" , "You only live -- (film)" , "Double in quantity" .)

I've seen this clue in The Independent.
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