It holds large quantity of alcohol still ultimately doubled (4)
I believe the answer is:
butt
'it holds large' is the definition.
The definition suggests a singular noun which matches the answer.
'quantity of alcohol still ultimately doubled' is the wordplay.
I cannot really see how this works, but
'quantity' could be 't' (T is an example) and 't' is present in the answer.
'still' could be 'but' (both can mean nonetheless or even so) and 'but' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for butt that I've seen before include "Strike with head" , "Water-cask; object of derision" , "Knock head" , "Blunt end - target of ridicule - hit with the head - cask - US backside" , "bum..." .)