Pouch completely empty, by the way (4)
I believe the answer is:
cyst
'pouch' is the definition.
(I've seen this before)
'completely empty by the way' is the wordplay.
'empty' suggests removing the centre.
'by the way' becomes 'st' (I've seen this in other clues).
'completely' with its centre taken out is 'cy'.
'cy'+'st'='CYST'
(Other definitions for cyst that I've seen before include "Fluid filled sac" , "Membrane" , "Sac in the body containing liquid secretion" , "Abnormal sac formed on or in the body" , "Subcutaneous sac" .)