The most common and most likely answer to this crossword clue is the 9 letter word SPLASHING
I've seen this crossword clue in The Daily Telegraph
S
P
L
A
S
H
I
N
G
Buddy explains!

The straight part
We know that "Washing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case washing = splashing.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 SPLASHING mean?
SPLASHING verb- To hit or agitate liquid so that part of it separates from the principal liquid mass.
- To disperse a fluid suddenly; to splatter.
- To hit or expel liquid at
- To create an impact or impression; to print, post or publicize prominently.
- To spend (money)
- To launch a ship.
- To stab (a person), causing them to bleed.
- An action that splashes.