Tube is heading north, getting call to leave east (6)
I believe the answer is:
siphon
'tube' is the definition.
(I know that siphon is a type of tube)
'north getting call to leave east' is the wordplay.
'north getting' becomes 'si' (I can't explain this - if you can you should believe this answer much more).
'call' becomes 'phone' (phone can mean to call by telephone).
'to leave' is a deletion indicator.
'east' becomes 'E' (synonyms).
'phone' with 'e' removed is 'phon'.
'si'+'phon'='SIPHON'
'is heading' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for siphon that I've seen before include "Tube used to remove liquid from a higher to a lower level" , "Soda dispenser" , "Bottle from which a liquid is forced by pressure of gas" , "A bottle that squirts, say soda water" , "Tube drawing off liquid" .)