Doctor, say, drawn to singular contents of used bottle? (5)
I believe the answer is:
dregs
'contents of used bottle?' is the definition.
'doctor say drawn to singular' is the wordplay.
'doctor' becomes 'dr' (synonyms).
'say' becomes 'eg'.
'drawn to' is a charade indicator (letters next to each other).
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'dr'+'eg'+'s'='DREGS'
(Other definitions for dregs that I've seen before include "Sediment, grounds" , "Parts of least value" , "Residue, lees" , "Fluid remnants" , "Liquid remnants with sediment" .)