It's useful for pouring fuel out, apparently (6)
I believe the answer is:
funnel
'it's useful for pouring' is the definition.
I can't tell whether this defines the answer.
'fuel out apparently' is the wordplay.
'out' means one lot of letters goes inside another.
'apparently' becomes 'nn' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'fuel' placed around 'nn' is 'FUNNEL'.
Can you help me to learn more?
(Other definitions for funnel that I've seen before include "Metal chimney on steamship" , "Conical utensil with narrow and wide ends" , "Kind of tube for pouring wide at top and narrow at bottom" , "Steam engine chimney" , "Stack" .)