Cop on trail of ecstasy drew blank (7)
I believe the answer is:
emptied
'blank' is the definition.
Both the definition and answer are adjectives. Maybe there's an association between them I don't understand?
'cop on trail of ecstasy drew' is the wordplay.
I cannot quite understand how this works, but
'ecstasy' could be 'e' (informal term for the drug) and 'e' is located in the answer.
'drew' could be 'tied' ('tie' can be a synonym of 'draw') and 'tied' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for emptied that I've seen before include "Discharged" , "Exhausted" , "was draining" , "Drained" , "Made void" .)