The most common and most likely answer to this crossword clue is the 5 letter word ELUTE
E
L
U
T
E
More clues leading to the result ELUTE
Buddy explains!

The straight part
We know that "wash" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wash = elute.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ELUTE mean?
ELUTE verb- To separate one substance from another by means of a solvent; to wash; to cleanse.