What does the cryptic crossword clue "Neck about 8 pints (6)" mean?

The wordplay uses a charade (building blocks). GALL (synonym="insolence, neck") + ON (synonym="about") = GALLON The answer is GALLON.

Neck about 8 pints (6)

Guardian Cryptic #29486 | 13 Across | 2024-09-12 flower