What does the cryptic crossword clue "Cheap liquor that's taken by fly-by-nights? (3-3)" mean?

The definition is "Cheap liquor". The wordplay uses a double definition. Double definition The answer is REDEYE.

Cheap liquor that's taken by fly-by-nights? (3-3)

Guardian Cryptic #29089 | 6 Down | 2023-06-06 flower