Sea dog in dark sticky liquid (3)
I believe the answer is:
tar
This might be a double definition.
'sea dog' is the first definition.
(I know that sea dog can be written as tar)
'dark sticky liquid' is the second definition.
'tar' can be an answer for 'liquid' (I have seen 'Black liquid' mean 'tar' so perhaps 'liquid' could also mean 'tar'). I am unsure of the 'dark sticky' bit.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tar that I've seen before include "'Thick, dark, sticky liquid (3)'" , "Cigarette residue - old word for sailor" , "Art (anag.)" , "Sailor; bitumen" , "Viscous liquid; sailor" .)