Sound method to get water extracted from milk (4)
I believe the answer is:
whey
'milk' is the definition.
(I have seen 'Watery milk ' mean 'whey' so perhaps 'milk' could also mean 'whey')
'sound method' is the wordplay.
'sound' indicates a 'sounds like' (homophone) clue.
'method' becomes 'way' (way of doing something).
'way' sounds like 'WHEY'.
'to get water extracted from' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for whey that I've seen before include "Milk serum" , "Watery part of milk after curd separation" , "Watery residue of milk" , "Residue from junket" , "Milky residue" .)