Consuming gallon, bound to swell (5)
I believe the answer is:
surge
'to swell' is the definition.
(I've seen this before)
'consuming gallon bound' is the wordplay.
'consuming' is an insertion indicator.
'gallon' becomes 'g' (abbreviation for the unit of liquid).
'bound' becomes 'sure' (synonyms).
'g' placed within 'sure' is 'SURGE'.
(Other definitions for surge that I've seen before include "Eddy" , "Rapidly rising water" , "Sudden increase in power" , "Rapid increase; powerful movement" , "Sudden powerful increase" .)