Salt, it needs putting in container (7)
I believe the answer is:
citrate
'salt' is the definition.
(I know that citrate is a type of salt)
'putting in container' is the wordplay.
'putting' becomes 'it' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'container' becomes 'crate' (crate is a type of container).
'it' going within 'crate' is 'CITRATE'.
'it needs' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Another definition for citrate that I've seen is " Salt".)