The present invention provides a method for efficiently and uniformly treating articles with two or more fluids without transferring the articles from one container to another container. The method comprises: providing the fluids, one at a time, to treat the articles (10) in a treatment system, wherein the treatment system comprises one or more trays (20) each of which has one or more baskets, each basket capable of holding one article (10), and wherein said trays (20) are stacked to form a vessel or are stacked and placed within a preformed vessel (140), said vessel or preformed vessel comprising a first entrance/exit (45,145) and a second entrance/exit (55,155)for the fluids; and each time one of the fluids is provided to treat the articles, (a) flushing continuously the articles with the fluid in a first flow direction from the first entrance/exit to the second entrance/exit, (b) reversing the flow direction of the fluid, (c) flushing continuously the articles with the fluid in a second direction from the second entrance/exit to the first entrance/exit for a second period of time, and (d) if necessary, repeating steps (a) to (c) for a desired number of times.