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

I believe the answer is:

torrential

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'bucketing down' is the definition.
I can't tell whether this definition defines the answer.

'rotten liar's rubbish' is the wordplay.
'rubbish' indicates an anagram (a poor quality or rubbish spelling of the letters).
'rotten'+'liar'='rottenliar'
'rottenliar' with letters rearranged gives 'TORRENTIAL'.

'is' is the link.

Can you help me to learn more?

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

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

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