Carrier indicates contents of tube are ruined (6)
I believe the answer is:
bearer
'carrier' is the definition.
(I know that carrier can be written as bearer)
'contents of tube are ruined' is the wordplay.
'contents of' indicates a hidden word.
'BEARER' is hidden within 'tube are ruined'.
'indicates' is the link.
(Other definitions for bearer that I've seen before include "Mourner carrying the coffin at a funeral" , "He helps to carry something - sometimes a coffin" , "Messenger - coffin-carrier" , "agent" , "He presents bill" .)