Dirty little thing, wader in the Channel?
I believe the answer is:
guttersnipe
'the channel?' is the definition.
Both the answer and definition are singular nouns.
Maybe you can see a link between them that I can't see?
'dirty little thing wader' is the wordplay.
'dirty little thing' becomes 'gutter' (I am not sure about this - if you are sure you should believe this answer much more).
'wader' becomes 'snipe' (snipe is a kind of wader).
'gutter'+'snipe'='GUTTERSNIPE'
'in' is the link.
Can you help me to learn more?
(Other definitions for guttersnipe that I've seen before include "Wretched child" , "(Neglected) child of the streets" , "Person behaving as one brought up in squalor" , "poor kid" , "Street urchin" .)