Lager, large tin, found in wharf (7)
I believe the answer is:
pilsner
'lager' is the definition.
(type of lager)
'large tin found in wharf' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'found in' indicates putting letters inside.
'wharf' becomes 'pier' (I've seen this before).
'l'+'sn'='lsn'
'lsn' going within 'pier' is 'PILSNER'.
(Other definitions for pilsner that I've seen before include "Czech beer" , "drink" , "alcohol" , "Bar tab might include this" , "Type of lager" .)