Dialysis-related complications have become a major concern as the number of patients receiving long-term maintenance dialysis increases. One cause of complications is contamination of the dialysis fluid. When dialysis fluid contaminated by bacteria or endotoxin (ET) or both has been used for a long time, cytokine production in vivo is enhanced and can lead to such complications as dialysis amyloidosis. The rate of dialysis-related complications might be reduced with a hemopurification method that uses a large amount of dialysis fluid as a substitution fluid (on-line hemodiafiltration) or an efficient dialyzer with enhanced internal filtration in which the dialysis fluid returns to the body as a replacement fluid; however, at the same time, there is an increased risk of ET entering the body because the dialysis fluid might be contaminated. Therefore, the dialysis fluid must be made aseptic, and the dialysis fluid line must be properly managed to prevent contamination of the dialysis fluid. A half-opened line is at great risk of contamination by living microbes, which can grow in dead spaces and where the flow of dialysis fluid is interrupted. The management of couplers is an important measure for maintaining cleanliness at the end of the dialysis fluid flow. We attempted to separate and regularly clean the main body of the coupler with ultrasonic equipment as a method of managing the conventional coupler. Using improved types of coupler, the water quality of the postcoupler flow was maintained at a level as high as that of the precoupler flow for the duration of the evaluation period without separate cleansing being done. Although separate once-a-week cleansing of the conventional coupler was able to keep ET values less than the detection limit, viable cell counts were unstable. On the other hand, twice-a-week ultrasonic cleansing eliminated almost all viable cells. No definite difference in ET values or viable cell counts was found between the cleansing groups, and ultrasonic cleansing was able, by itself, to provide a sufficient cleansing effect. We conclude that ultrasonic cleansing of conventional couplers is a useful method for maintaining the water quality of the postcoupler flow because the cleansing of the coupler twice or more a week is sufficient to keep the water quality of the postcoupler flow as high as that of the precoupler flow.