Squeeze gallons into the tin, furiously (7)
I believe the answer is:
tighten
'squeeze' is the definition.
(tighten can mean to squeeze or contract)
'gallons into the tin furiously' is the wordplay.
'gallons' becomes 'g' (abbreviation).
'into' indicates putting letters inside.
'furiously' indicates an anagram.
'the'+'tin'='thetin'
'thetin' anagrammed gives 'tihten'.
'g' put inside 'tihten' is 'TIGHTEN'.
(Other definitions for tighten that I've seen before include "contract" , "get tense" , "increase tension" , "Do this to your belt to economise (7)" , "Fasten more firmly" .)