What does the cryptic crossword clue "Alteration of crest in tank (7)" mean?

The definition is "tank". The wordplay uses an anagram. anagram of CREST + IN = CISTERN; definition: "tank" The answer is CISTERN.

Alteration of crest in tank (7)

Daily Mail Cryptic #17121 | 24 Across | 2023-06-16 flower