Black slimy stuff found in drink (5)
I believe the answer is:
booze
'drink' is the definition.
(I know that drink can be written as booze)
'black slimy stuff' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'slimy stuff' becomes 'ooze' (I've seen this in another clue).
'b'+'ooze'='BOOZE'
'found in' acts as a link.
(Other definitions for booze that I've seen before include "Consume alcohol" , "Alcoholic liquor" , "Alcoholic drink generally" , "Alcohol (colloq.)" , "Drink to excess (colloq.)" .)