A sieve device (1) for untreated drilling mud being brought up from a well and a method for use is provided. The sieve device (1) has a filter device (3) to separate a share of the drilling liquid from the drill cuttings. The sieve device (1) connects to a first outlet that receives drilling cuttings held back on the filter device (3) and a second outlet (11) that receives drilling liquid flowing from the filter device (3). The sieve device (1) also has at least one secondary filter (13) to separate drill cuttings from drilling liquid, a filter guard (17) being arranged in connection with the secondary filter (12), and a bypass arrangement (19) by means of which the filter guard (17) is arranged to open for communication of untreated drilling mud held back on the secondary filter (13), into the second outlet (11) for drilling liquid.