Valve and set of pipes next to bunk (8)
I believe the answer is:
stopcock
'valve' is the definition.
(type of valve)
'set of pipes next to bunk' is the wordplay.
'set of pipes' becomes 'stop' (set of organ pipes).
'next to' says to put letters next to each other.
'bunk' becomes 'cock' (both can mean nonsense).
'stop'+'cock'='STOPCOCK'
'and' is the link.
(Other definitions for stopcock that I've seen before include "Isolating valve in pipework" , "water regulator" , "Valve in water supply" , "Control of flow in pipe" , "bit of plumbing" .)