Rotten liar's bilge is bucketing down! (10)

I believe the answer is:

torrential

I'm a little stuck... Click here to teach me more about this clue!

'down' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?

'rotten liar's bilge is bucketing' is the wordplay.
'rotten liar' can be anagrammed to 'TORRENTIAL'.
However, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for torrential that I've seen before include "Like heavy fall" , "Pelting" , "driving" , "Flowing overwhelmingly" , "(Of rain) falling copiously" .)

I've seen this clue in the Sydney Morning Herald.

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