It's his job to feed the flaming thing! (6)
I believe the answer is:
stoker
'it's his job to feed the flaming thing' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'it's his job to feed' is the wordplay.
'it's his job' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to' means one lot of letters go next to another (I've seen this in other clues).
'feed' becomes 'stoke' (I've seen this in another clue).
'r' put after 'stoke' is 'STOKER'.
Can you help me to learn more?
(Other definitions for stoker that I've seen before include "One tends to fire" , "One feeding furnace" , "One tending furnace" , "He's fuelled < the legend of Dracula" , "Writer" .)