The most common and most likely answer to this crossword clue is the 1 plus 5 plus 14 letter word 4 WATER BUTT/FOREGOING
I've seen this crossword clue in The Guardian
4
W
A
T
E
R
B
U
T
T
/
F
O
R
E
G
O
I
N
G
Buddy explains!
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.