Rubbish sparkling wine mostly drunk by partners (5)
I believe the answer is:
waste
'rubbish' is the definition.
(I know that rubbish can be written as waste)
'sparkling wine mostly drunk by partners' is the wordplay.
'sparkling wine' becomes 'asti' (I've seen this before).
'mostly' means to remove the last letter.
'drunk by' means one lot of letters goes inside another.
'partners' becomes 'we' (West and East are partners in the game bridge).
'asti' with its last letter taken off is 'ast'.
'ast' inserted within 'we' is 'WASTE'.
(Other definitions for waste that I've seen before include "Use to no purpose" , "Fail to use (profitably)" , "Use inefficiently or inappropriately" , "kill" , "unused" .)