Porter blended into filling drink (7)
I believe the answer is:
janitor
'porter' is the definition.
(thesaurus)
'blended into filling drink' is the wordplay.
'blended' is an anagram indicator.
'filling' is an insertion indicator.
'drink' becomes 'jar' (colloquial).
'into' with letters rearranged gives 'nito'.
'nito' going inside 'jar' is 'JANITOR'.
(Other definitions for janitor that I've seen before include "(In Scotland) school caretaker" , "Caretaker or doorkeeper" , "One employed to clean and maintain a building" , "Person looking after building" , "Caretaker (mainly US)" .)