Went back in ocean (4)
I believe the answer is:
deep
'ocean' is the definition.
(I know that deep is a type of ocean)
'went back' is the wordplay.
'went' becomes 'peed' (both can mean urinated).
'back' shows that the letters should be reversed in order.
'peed' reversed gives 'DEEP'.
'in' is the link.
(Other definitions for deep that I've seen before include "greatly involved?" , "Bottomless" , "Main" , "Heartfelt" , "(Of sound) low in pitch" .)