Pipe is monster not drained (7)
I believe the answer is:
hydrant
'pipe' is the definition.
(I know that hydrant is a type of discharge pipe)
'monster not drained' is the wordplay.
'monster' becomes 'hydra' (Hydra is an example).
'drained' says to hollow out the word (remove centre letters).
'not' with its middle removed is 'nt'.
'hydra'+'nt'='HYDRANT'
'is' is the link.
(Other definitions for hydrant that I've seen before include "It connects a hose to the water main" , "Water point for firefighters" , "Water tap for drawing from the mains" , "Pipe on the street for the fire brigade" , "Fire hose supplier" .)