Container for all that old brass (7)
I believe the answer is:
sackbut
'old brass' is the definition.
'sackbut' can be an answer for 'brass' (sackbut is a kind of brass). I am unsure of the 'old' bit.
'container for all' is the wordplay.
'container' becomes 'sack' (sack is a kind of container).
'for all' becomes 'but' (I can't justify this - if you can you should believe this answer much more).
'sack'+'but'='SACKBUT'
'that' is the link.
Can you help me to learn more?
(Other definitions for sackbut that I've seen before include "one on the slide" , "music maker" , "Medieval form of trombone" , "Old instrument" , "Musical instrument of the Renaissance" .)