The most common and most likely answer to this crossword clue is the 4 plus 5 letter word COME CLEAN
I've seen this crossword clue in The Guardian
C
O
M
E
C
L
E
A
N
Buddy explains!
The straight part
We know that "Reveal all and sing/it’s what we should do in the shower" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reveal all and sing/it’s what we should do in the shower = come clean.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.