down the tubes

• down the tubes: 失敗に終わる

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• And if we're right that the Tattler is the medium and we make up a reply based on what we have in this note and screw it up —— if it doesn't look right to him —— we're down the tubes.
  （『タトラー』が通信手段だという予想が当たってて、あの手紙の内容をもとに返事をでっち上げて失敗したら――やつに怪しまれたら――まあそれでこの手はおしまいだ。）
  Thomas Harris, Red Dragon, Berkley Books, ch. 14