Opening for a chap in the sanitation department (7)
I believe the answer is:
manhole
'the sanitation department' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'opening for a chap' is the wordplay.
'opening' becomes 'hole' (hole is a kind of opening).
'for' means one lot of letters go next to another (I've seen this in other clues).
'a chap' becomes 'man' (chap can mean a man).
'hole' put after 'man' is 'MANHOLE'.
'in' is the link.
Can you help me to learn more?
(Other definitions for manhole that I've seen before include "Opening with a cover giving access underground" , "Drain cover" , "Underground access point" , "Access chamber to sewer or drain" , "Street access cover" .)