See about US serving man turning tap on barrel (6)
I believe the answer is:
spigot
'tap on barrel' is the definition.
(I've seen this before)
'see about us serving man turning' is the wordplay.
'see about' is an insertion indicator.
'us' becomes 'tops' (I can't justify this - if you can you should believe this answer much more).
'serving man' becomes 'gi' (GI can mean an American soldier).
'turning' is a reversal indicator.
'tops' going around 'gi' is 'togips'.
'togips' backwards is 'SPIGOT'.
Can you help me to learn more?
(Other definitions for spigot that I've seen before include "Small peg or plug" , "Tap, faucet" , "It's a water tap in America" , "Peg to control the flow of a tap" , "Beer tap" .)