multi - tank dishwashers are used , in particular , industrially , in order to clean items which are to be washed . the invention relates to a multi - tank dishwasher which is provided with a washing area . the washing area comprises at least one rinsing water storage tank , at least one filter housing , at least one fine filter and at least one backwash device . in the normal mode , a filter wall of the at least one fine filter is cross flown in the direction from a waste water chamber to a pure water chamber . in order to clean the fine filter , the multi - tank dishwasher can be operated in a backwashing mode , without interrupting the washing process . in said backwashing mode , a cross - flow of the at least one filter wall of the rinsing water is reversed by using a backwash pump and a waste water pump . dirt particles , which are located on the inner side of the filter wall , are rinsed off and are removed by the waste water pump in the waste water outlet .