 Vacuum sewer systems may be selected for their fast (avoiding conflicts with traffic and tourism), cost-effective and flexible installation.Examples include Flavigny-sur-Ozerain, France, and Khasab and Al Seeb in Oman.Vacuum sewer systems can be set up so that they collect concentrated blackwater (toilet wastewater) only, with the greywater from sinks and baths being collected separately (it is much easier to treat greywater than blackwater).