Person who fights in small toilet (8)
I believe the answer is:
scrapper
'person who fights' is the definition.
'scrapper' can be an answer for 'person' (scrapper is a kind of person). I am not certain of the rest of the definition.
'small toilet' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'toilet' becomes 'crapper' (synonyms).
's'+'crapper'='SCRAPPER'
'in' is the link.
Can you help me to learn more?
(Other definitions for scrapper that I've seen before include "Boxer" , "An informal fighter - sounds ragged" , "An informal fighter, or one who discards waste" , "someone fighting" , "I get shot of something" .)