Hook up bucket down after flipping over (4)
I believe the answer is:
meet
'hook up' is the definition.
(I've seen this in another clue)
'bucket down after flipping over' is the wordplay.
'bucket down' becomes 'teem' (both can mean to rain).
'after flipping over' says the letters should be written backwards.
'teem' reversed gives 'MEET'.
(Other definitions for meet that I've seen before include "Assemble" , "Satisfy (requirements)" , "Attend" , "Get together socially or for business" , "Encounter - suitable - pay" .)