Clip oddly put on rear tank (7)
I believe the answer is:
cistern
'tank' is the definition.
(cistern is a kind of tank)
'clip oddly put on rear' is the wordplay.
'oddly' means one should take alternating letters.
'put on' is a charade indicator (letters next to each other).
'rear' becomes 'stern' (stern is a kind of rear**).
The alternate letters of 'clip' are 'ci'.
'ci'+'stern'='CISTERN'
(Other definitions for cistern that I've seen before include "Water tank for toilet" , "Vat" , "Tank - sac of body fluid" , "Toilet water reservoir" , "Toilet tank [ital]" .)