Bowel in knots — that's a bender! (5)
I believe the answer is:
elbow
'that's a bender' is the definition.
(something which bends)
'bowel in knots' is the wordplay.
'in knots' indicates anagramming the letters (I've seen this in other clues).
'bowel' is an anagram of 'ELBOW'.
(Other definitions for elbow that I've seen before include "Sort of grease" , "Nudging joint?" , "Nudge" , "Hinge joint" , "Barge" .)