Abstract: A water closet system comprising a lavatory which is connected to a collection tank or mouldering chamber (2) over a discharge piping (3), and a liquid separator (4) interconnected in said discharge piping (3) adjacent and above the tank or chamber (2). The liquid separator (4) comprises an inlet pipe (8) having a widened bottom portion (13), an outlet pipe (9) preferably having a widened top portion (14) and a liquid container which sealingly encloses at least the end portions (13, 14) of said inlet and outlet pipes (8, 9). The diameter (D2) of the top end (14) of the outlet pipe (9) is equal to of larger than the diameter (D1) of the non-widened portion of the inlet pipe (8), and the said diameter (D3) of the bottom end (13) of the inlet pipe (8) is larger than said diameter (D2) of the top portion (14) of the outlet pipe (9).