The most common and most likely answer to this crossword clue is the 9 letter word SHOWERING
I've seen this crossword clue in The Guardian
S
H
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More clues leading to the result SHOWERING
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 = showering.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 SHOWERING mean?
SHOWERING verb- (followed by with) To spray with (a specified liquid).
- To bathe using a shower.
- To bestow liberally, to give or distribute in abundance
- To rain in a shower; to cascade down.
- Something that falls in a shower.