Lead pipe prisoner sits on (7)
I believe the answer is:
conduct
'lead' is the definition.
(I know that lead can be written as conduct)
'pipe prisoner sits on' is the wordplay.
'pipe' becomes 'duct' (I've seen this in another clue).
'prisoner' becomes 'con' (abbreviation for 'convict').
'sits on' says to put letters next to each other.
'duct' after 'con' is 'CONDUCT'.
(Other definitions for conduct that I've seen before include "Behaviour; transmit" , "Guide - behaviour" .)