Tell you what firefighters do? Oh, buzz off! (2,2,6)
I believe the answer is:
go to blazes
'tell you what firefighters' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'do? oh buzz off' is the wordplay.
I cannot really see how this works, but
'do?' could be 'go' (doing is a kind of going) and 'go' is found in the answer.
'oh' could be 'o' and 'o' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for go to blazes that I've seen before include "be damned" , "Firefighters will" , "Dismissive expression (referring to hell)" .)