Obstacle in shabby toilet makes one wee on foot (6,3)
I believe the answer is:
little toe
'one wee on foot' is the definition.
The definition suggests a singular noun which matches the answer.
'obstacle in shabby toilet' is the wordplay.
'obstacle' becomes 'let' ('let' could historically mean an obstruction).
'in' is an insertion indicator.
'shabby' is an anagram indicator.
'toilet' with letters rearranged gives 'littoe'.
'let' going inside 'littoe' is 'LITTLE TOE'.
'makes' is the link.
Can you help me to learn more?
(Other definitions for little toe that I've seen before include "Small digit" , "Tiniest foot digit" , "smallest digit" , "Lower extremity" .)