。
Champagne flowed all through the night.
Literal
Night-through champagne [subj-が] was-poured-and-exchanged-[passive-された].
酌み交わす ('pour for each other, exchange drinks') is a Sino-Japanese compound verb specific to drinking culture — the ritual of mutual pouring at social gatherings. Its passive form 酌み交わされる gives 'was poured and exchanged' — the party atmosphere abstracted from specific drinkers. シャンペン is from French 'champagne,' with the older spelling.