I am moving big bin when drinking (8)
I believe the answer is:
imbibing
'drinking' is the definition.
(I know that drinking can be written as imbibing)
'i am moving big bin' is the wordplay.
'i am' becomes 'I'm' (contraction).
'moving' is an anagram indicator (letters are moved around).
'big'+'bin'='bigbin'
'bigbin' with letters rearranged gives 'bibing'.
'im'+'bibing'='IMBIBING'
'when' is the link.
(Other definitions for imbibing that I've seen before include "Drinking alcohol" , "Taking drink" .)