Abstract: Systems for cleaning a storage tank and fluid hydrocarbons stored within the storage tank comprise: a vehicle for transporting the system between sites having said storage tanks; a fluid cleaning circuit mounted with respect to said vehicle for extracting fluid hydrocarbons from the storage tank for cleaning; a settlement tank mounted with respect to said vehicle to be in fluid communication with the fluid cleaning circuit to receive contaminated fluid hydrocarbons for separation by gravity; wherein the fluid cleaning circuit is controllable to clean the fluid hydrocarbons and the storage tank and to dispose of any waste material extracted from the fluid hydrocarbons during the cleaning process and following disposal of the waste material the fluid cleaning circuit is configured to convert the settlement tank into a non-volatile environment prior to the vehicle leaving the site.