Bucket brigade called out (4)
I believe the answer is:
teem
'bucket' is the definition.
(both can mean to rain)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for teem that I've seen before include "Bear" , "Rain hard" , "Abound, swarm with" , "(Of rain) pour down" , "Bucket down" .)