Eels swimming in what's left of the liquid (4)
I believe the answer is:
lees
'what's left of the liquid' is the definition.
I can't judge whether this defines the answer.
'eels swimming' is the wordplay.
'swimming' indicates anagramming the letters.
'eels' anagrammed gives 'LEES'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for lees that I've seen before include "Sediment from wine or beer production" , "Dregs, sediment" , "Sediment from fermentation of alcohol" , "Grounds" , "Wine at bottom of glass" .)