Back roads unevenly filled with mixed oil and tar (6)
I believe the answer is:
sailor
'tar' is the definition.
(I've seen this in another clue)
'back roads unevenly filled with mixed oil' is the wordplay.
'back' shows that the letters should be reversed in order.
'unevenly' means one should take alternating letters (letters in odd-numbered positions rather than even).
'filled with' is an insertion indicator.
'mixed' indicates an anagram.
The alternate letters of 'roads' are 'ras'.
'ras' reversed gives 'sar'.
'oil' with letters rearranged gives 'ilo'.
'sar' placed around 'ilo' is 'SAILOR'.
'and' is the link.
(Other definitions for sailor that I've seen before include "Member of a ship's crew" , "Jack" , "Person who goes to sea" , "Seafarer" , "Seaman" .)