Lowest point in drain in need of repair (5)
I believe the answer is:
nadir
'lowest point' is the definition.
'drain in need of repair' is the wordplay.
'in need of repair' indicates an anagram.
'drain' is an anagram of 'NADIR'.
'in' acts as a link.
(Other definitions for nadir that I've seen before include "lowest of the low" , "Point of greatest despair" , "least successful point" , "Drain to lowest level" , "Low point" .)