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 judge whether this definition defines the answer.
'fuel out apparently' is the wordplay.
'out' indicates putting letters inside.
'apparently' becomes 'nn' (I can't explain this - if you can you should believe this answer much more).
'fuel' going 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" .)