Difficult task primarily, to everyone collecting gold, diamond; exchequer is empty (4,5)
I believe the answer is:
tall order
'difficult task' is the definition.
(I've seen this before)
'primarily to everyone collecting gold diamond exchequer is empty' is the wordplay.
I cannot really see how this works, but
'everyone' could be 'all' (all people) and 'all' is located in the answer.
'to' is within the answer.
'empty' could be 'e' (abbreviation e.g. on guages) and 'e' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tall order that I've seen before include "demanding request" , "Difficult demand" , "Unreasonable demand" , "as the building of Babel was?" , "Lofty command - that's a difficult task" .)