Content of pop emptied through straw (5)
I believe the answer is:
happy
'content' is the definition.
(content can mean happy or pleased)
'pop emptied through straw' is the wordplay.
'emptied' suggests removing the centre.
'through' is an insertion indicator (inserted letters go through the word).
'straw' becomes 'hay' (I've seen this before).
'pop' with its centre taken out is 'pp'.
'pp' placed inside 'hay' is 'HAPPY'.
'of' is the link.
(Other definitions for happy that I've seen before include "Blissful" , "Fortunate - joyful" , "Pleased; fortunate" , "Contented" , "Gleeful" .)