Vapour has right flow (6)
I believe the answer is:
stream
'flow' is the definition.
(I know that flow can be written as stream)
'vapour has right' is the wordplay.
'vapour' becomes 'steam' (steam is a kind of vapour).
'has' is an insertion indicator.
'right' becomes 'r' (abbreviation).
'steam' going around 'r' is 'STREAM'.
(Other definitions for stream that I've seen before include "Steady flow; pupil group" , "'Current, flow (6)'" , "Flow of water on land" , "Brook, burn" , "Transmit music or video online" .)