Not allowed to reverse round the bend (3)
I believe the answer is:
out
'not allowed' is the definition.
(I've seen this before)
'to reverse round the bend' is the wordplay.
'reverse' is a reversal indicator.
'round' is an insertion indicator.
'the bend' becomes 'u' (a U-bend is a kind of bend - pipe under sink).
'to' reversed gives 'ot'.
'ot' placed around 'u' is 'OUT'.
(Other definitions for out that I've seen before include "Possibly caught" , "On strike - dismissed - unconsciousout" , "Inaccurate - dismissed" , "In error" , "sleeping" .)