A device for preventing foam or air bubbles from accumulating in a measuring zone of a turbidity sensor connected in a wash-water circuit of a dishwasher or washing machine includes a main flow conduit and a bypass conduit connected to the main flow conduit. The bypass conduit includes a first conduit section branching off from the main flow conduit, a second conduit section leading back into the main flow conduit at a junction, and an enlarged region of reduced flow velocity connected upstream of the junction. The enlarged region provides the measuring zone for the turbidity sensor, and includes a curved baffle and a downward-facing bulbous protuberance opposite the baffle so as to form a backflow region. The measuring zone is located within the backflow region in the bulbous protuberance.