could be a lengthy procedure. To facilitate applications for West Berliners seeking such Eastern visas, the GDR Foreign Ministry was later allowed to open Offices for the Affairs of Visits and Travelling () in West Berlin, which were not allowed to show any official symbols of East Germany. The Eastern officials working commuted every morning and evening between East and West Berlin. Their uniforms showed no official symbols except the name Büro für Besuchs- und Reiseangelegenheiten. They accepted visa applications and handed out confirmed visas issued in the East to the West Berlin applicants. A shed formerly housing one such Büro für Besuchs- und Reiseangelegenheiten can be found on Waterlooufer 5–7 in Berlin-Kreuzberg, close to Hallesches Tor underground station. Another form of traffic between East and West Berlin was the transfer of West Berlin's sewage into East Berlin and East Germany through the sewer pipes built in the late 19th and early 20th centuries. The sewage flowed into the East because most of the pre-war sewage treatment facilities, mostly sewage farms, happened to be in the East after the division of the city. Sewer pipes, however, once discovered as a way to flee the East, were blocked by bars. West Berlin paid for the treatment of its sewage in Western Deutsche Marks which were desperately needed by the East German government. Since the methods used in the East did not meet Western standards, West Berlin increased the capacity of modern sewage treatment within its own territory, such that the amount of its sewage treated in the East had been considerably reduced by the time the Wall came down. The situation with refuse was similar. The removal, burning or disposal of the ever-growing amount of West Berlin's rubbish became a costly problem, but here too an agreement was found since West Berlin would pay in Western Deutsche Marks. On 11 December 1974 East Germany and West Berlin's garbage utility company BSR signed a contract to dispose of refuse on a dump right beside the Wall in East German Groß-Ziethen (today a part of Schönefeld). An extra checkpoint, solely open for Western bin lorries (garbage trucks), was opened there. Later on, a second dump, further away, was opened in Vorketzin, a part of Ketzin. As for the S-Bahn, operated throughout Berlin by the East German Reichsbahn, the construction of the Wall meant a serious disruption of its integrated network, especially of the