Soak (up), as gravy (3)
I believe the answer is:
sop
'soak up as gravy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sop that I've seen before include "Concession given to mollify or placate" , "Bread dipped in gravy" , "usual way of doing things, initially" , "Concession of philosophy" , "A concession or bribe, once offered to Cerberus" .)