U2 singer keeps gallon in drum (5)
I believe the answer is:
bongo
'drum' is the definition.
(bongo is a kind of drum)
'u2 singer keeps gallon' is the wordplay.
'u2 singer' becomes 'Bono' (I've seen this in another clue).
'keeps' is an insertion indicator.
'gallon' becomes 'g' (abbreviation for the unit of liquid).
'bono' placed around 'g' is 'BONGO'.
'in' is the link.
(Other definitions for bongo that I've seen before include "Bucket-shaped drum - rare spiral-horned antelope" , "Hand-played drum" , "Type of drum - central African antelope" , "Hand drum" , "Throw; stopper" .)