The most common and most likely answer to this crossword clue is the 14 letter word BREAST-FEEDING
I've seen this crossword clue in The Guardian
B
R
E
A
S
T
-
F
E
E
D
I
N
G
Buddy explains!
The straight part
We know that "drinking" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case drinking = breast-feeding.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.