Twist tube into the trachea (8)
I believe the answer is:
windpipe
'the trachea' is the definition.
('windpipe' can be a synonym of 'trachea')
'twist tube' is the wordplay.
'twist' becomes 'wind' (synonyms).
'tube' becomes 'pipe' (pipe is a kind of tube).
'wind'+'pipe'='WINDPIPE'
'into' acts as a link.
(Other definitions for windpipe that I've seen before include "airline" , "The trachea is another name for this breathing passage" , "breathing space" , "Air passage to lungs, the trachea" , "The trachea, less formally" .)