Device for mixing the contents of a tank comprising a first pipe connecting body arranged on a connecting flange of a tank; a riser pipe extending through the first pipe connecting body into the tank; a mixing pipe extending through said first pipe connecting body into said tank; and a pump whose outlet can be connected at least to the mixing pipe and whose inlet can be connected both to the first pipe connecting body and to the riser pipe. Further a method for mixing the contents of a tank is claimed.