You can get 509, that is, in a mess tin (5)
I believe the answer is:
dixie
'a mess tin' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'you can get 509 that is' is the wordplay.
I cannot really understand how this works, but
'that is' could be 'ie' (short for Latin 'id est', 'that is') and 'ie' is located in the answer.
The remaining letters 'dix' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for dixie that I've seen before include "The Deep South" , "Confederate States of America" , "American League?" , "Pan" , "Southern states that seceded from the USA in 1861" .)