Search for a solution once Sark's wrecked with British downpours (4,4,6)
I believe the answer is:
rack ones brains
'search for a solution' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'once sark's wrecked with british downpours' is the wordplay.
'wrecked with' indicates an anagram.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'downpours' becomes 'rains' (I've seen this in another clue).
'once'+'sark'='oncesark'
'oncesark' with its letters anagrammed with 'b' makes 'rackonesb'.
'rackonesb'+'rains'='RACK ONES BRAINS'
Can you help me to learn more?
(Other definitions for rack ones brains that I've seen before include "trying to 1 across [RECALL] - with 22d" , "Think very hard" , "Make a great effort to remember" .)