Landrath, "Die Rohrpost-Anlage in Berlin und Charlottenburg." Archiv für Post und Telegraphie , Vol. 16, No. 12, Jun. 1888, pp. 354-369 describes, among other items, the initial version of Berlin's pneumatic post system. This was built by Siemens & Halske and became operational on November 18, 1865. On page 358, he discusses a major design flaw (bolding mine; otherwise all of the original spelling and typography have been retained):
Ein wesentlicher Fehler in der Ausführung bestand darin, daſs die Röhren nicht überall in ausreichender Tiefe unter dem Pflaster lagen. In Folge dieses Umstandes kam es sehr häufig vor, daſs bei Pflasterungen der Straſsen, Instandsetzungen und Neuanlagen der Gas- und Wasserleitungen u.s.w. die Röhren von Arbeitern mit der Hacke angehauen wurden, was vielfach Entstellungen des Querschnittes der Röhren und damit Störungen im Betriebe zur Folge hatte. Aus der gleichen Ursache wurde im Winter, oft bei nur wenige Tage anhaltender strengerer Kälte, der Betrieb durch Eisbildungen in den Röhren nicht selten Tage lang gestört. In solchen Fällen wurden zur Ablösung des Eises von den Rohrwänden verhältniſsmäſsig groſse Mengen flüssigen Weingeistes in die Röhren eingeführt. Das losgelöste Eis wurde durch einen mittels erhöhten Druckes zum Oefteren durch die Rohrleitung hindurchgetriebenen, mit Bürsten besetzten Kolben nach und nach aus den Röhren beseitigt.
My translation: "A substantial defect of the installed system was that the tubes were not always laid at sufficient depth below the pavement. As a consequence of this circumstance it happened frequently that during the paving of streets, the repair and new installation of gas and water lines, etc., the pipes were damaged by workers with
hoes, which lead to frequent distortion of the cross section of the pipes, resulting in service outages. For the same reason operations were disrupted during winter,
frequently after just a few days of continuous severe cold, by ice forming in the tubes. In such cases relatively large amounts of spirits of wine were introduced into the tubes to detach the ice from the tube walls. The dislodged ice was then gradually removed from the pipes by a brush-studded piston that was repeatedly driven through the line with increased pressure."
For the translation of "Weingeist", I relied on William James, A Complete Dictionary of the English and German Languages, Leipzig: B. Tauchnitz 1882, to accurately capture the sense of the word at the time of the publication above. As other answers have pointed out, spirits of wine refers to a mixture of ethanol and water; the product of distillation.
Other literature I consulted (see list below) does not mention this particular method of cleaning. It therefore seems likely that the above publication is the origin of the information cited in the question and that at some point someone confused spirits of wine with wine. I note that descriptions of the pneumatic post system in Berlin after it became available to the general public in 1875 point out that the air introduced into the tubes is cooled and dehumidified to prevent the formation of ice which is of particular importance as the extended system utilized various bridges where the tubes were directly exposed to the air.
Pennrich, "Die Rohrpost-Einrichtungen in Berlin." Archiv für Post und Telegraphie, Vol. 4, No. 23, Dec. 1876, pp. 705-714
Hellwig, "Pneumatische Erscheinungen beim Rohrpostbetrieb."
Archiv für Post und Telegraphie , Vol. 6, No. 10, May 1878, pp. 289-301
Grose, "Beschreibung der Rohrpostanlage in Berlin." Der Bär. Illustrierte Berliner Wochenschrift, Vol. 6, 1880, pp. 92-96
O. Veredarius, Das Buch von der Weltpost. Berlin: Herm. J. Meidinger 1885.
"Rohrpost", pp. 197-203
