Soap chemical (3)
I believe the answer is:
lye
'soap chemical' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lye that I've seen before include "Alkaline solution used for washing" , "solution that comes out in the wash?" , "Solution obtained by leaching" , "Strongly alkaline solution for washing or cleansing" , "Strong alkaline solution" .)