Wastes like fat and the content of skimming tanks are usually classified "controlled waste", and their disposal is placed in the hands of authorized companies who specialize in this type of waste disposal.

In Switzerland, disposal of controlled waste is subject to regulations like the waste management act. You will find addresses of waste disposal companies and more information here:

www.abfall.ch

For information on EU countries, you may find this website helpful:

http://europa.eu/legislation_summaries/environment/waste_management/index_en.htm