Methinks there's no writing fluid. (Somebody's drunk it?) (5)
I believe the answer is:
meths
'somebody's drunk it?' is the definition.
I can't judge whether this defines the answer.
'methinks there's no writing fluid' is the wordplay.
'there's no' is a deletion indicator.
'writing fluid' becomes 'ink' (fluid used for writing).
'methinks' with 'ink' removed is 'METHS'.
Can you help me to learn more?
(Other definitions for meths that I've seen before include "Spirit" , "Methylated spirits (colloq.)" , "Fuel" , "Violet-coloured alcohol" , "unsuitable alcohol" .)