Forget name and choose to drink gallons (7)
I believe the answer is:
neglect
'forget' is the definition.
(I've seen this before)
'name and choose to drink gallons' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'and' is a charade indicator (letters next to each other).
'choose' becomes 'elect' (electing is a kind of choosing**).
'to drink' means one lot of letters goes inside another.
'gallons' becomes 'g'.
'elect' going around 'g' is 'eglect'.
'n'+'eglect'='NEGLECT'
(Other definitions for neglect that I've seen before include "Leave unattended, disregard" , "Give little attention to" , "slight" , "Disuse" , "Fail to look after (something)" .)