Truck seen outside large boozer (7)
I believe the answer is:
tippler
'boozer' is the definition.
(I've seen this before)
'truck seen outside large' is the wordplay.
'truck' becomes 'tipper' (I've seen this before).
'seen outside' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'tipper' going around 'l' is 'TIPPLER'.
(Other definitions for tippler that I've seen before include "Boozer" , "Person who drinks constantly in small amounts" , "Imbiber" , "Drunk" , "One habitually drinking" .)