I follow vocal instruction to extract sap from coniferous wood? (9)

'extract sap from coniferous wood?' is the definition.
The definition suggests a singular noun which matches the answer.

'i follow vocal instruction' is the wordplay.
I cannot quite see how this works, but
'follow' could be 'succeed' (synonyms) and 'succeed' is present in the answer.
The remaining letters 'er' 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).

'to' acts as a link.

Can you help me to learn more?