Get on board as ten shot bucket down (7)
I believe the answer is:
entrain
'get on board' is the definition.
(I've seen this in another clue)
'ten shot bucket down' is the wordplay.
'shot' is an anagram indicator.
'bucket down' becomes 'rain' (I am not sure about this - if you are sure you should believe this answer much more).
'ten' with letters rearranged gives 'ent'.
'ent'+'rain'='ENTRAIN'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for entrain that I've seen before include "Get on board railway carriages" , "Sweep along" , "Bring about as consequence" , "Pop on the coach" , "Get on a rail service" .)