What does the cryptic crossword clue "Something big in the drink — a drink swallowed by idiot (8)" mean?

The definition is "Something big in the drink". The wordplay uses a cryptic definition. Cryptic definition The answer is CACHALOT.

Something big in the drink — a drink swallowed by idiot (8)

Times Cryptic #28966 | 16 Across | 2024-07-11 flower