The Polish rights were as follows:
The Versailles Treaty June 28, 1919
The Principal Allied and Associated Powers undertake to negotiate a Treaty between the Polish Government and the Free City of Danzig, which shall come into force at the same time as the establishment of the said Free City, with the following objects:
To effect the inclusion of the Free City of Danzig within the Polish Customs frontiers, and to establish a free area in the port;
To ensure to Poland without any restriction the free use and service of all waterways, docks, basins, wharves and other works within the territory of the Free City necessary for Polish imports and exports;
To ensure to Poland the control and administration of the Vistula and of the whole railway system within the Free City, except such street and other railways as serve primarily the needs of the Free City, and of postal, telegraphic and telephonic communication between Poland and the port of Danzig;
To ensure to Poland the right to develop and improve the waterways, docks, basins, wharves, railways and other works and means of communication mentioned in this Article, as well as to lease or purchase through appropriate processes such land and other property as may be necessary for these purposes,
To provide against any discrimination within the Free City of Danzig to the detriment of citizens of Poland and other persons of Polish origin or speech;
To provide that the Polish Government shall undertake the conduct of the foreign relations of the Free City of Danzig as well as the diplomatic protection of citizens of that city when abroad.
A lof of free stuff that would otherwise be pricey.