Spend a night in a filthy place outside (4)
I believe the answer is:
stay
'spend a night' is the definition.
I can't judge whether this defines the answer.
'a filthy place outside' is the wordplay.
'filthy place' becomes 'sty' (I've seen this before).
'outside' is an insertion indicator (some letters go outside others).
'a' placed within 'sty' is 'STAY'.
'in' is the link.
Can you help me to learn more?
(Other definitions for stay that I've seen before include "Guy rope" , "guy giving > support" , "Defer" , "Supporting rod" , "Remain; suspend" .)