Last bit of craft in work, going back and forth (4)
I believe the answer is:
poop
'last bit of craft' is the definition.
(part of a ship)
'work going back and forth' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'going back' shows that the letters should be reversed in order.
'and' says to put letters next to each other.
'forth' becomes 'op' (I am not sure about this - if you are sure you should believe this answer much more).
'op' in reverse letter order is 'po'.
'po'+'op'='POOP'
'in' is the link.
Can you help me to learn more?
(Other definitions for poop that I've seen before include "Palindromic part of a ship" , "raised structure" , "High deck at old sailing ship's stern" , "Exhaust" , "Highest deck of ship" .)