Suction device for wastewater tank, comprising: - a suction channel (1043, 10143, 10243, 10443) extending from a suction connection flange formed for attachment in the region of an opening of the wastewater tank to a suction opening, - a connection coupling extending from the suction connection flange, wherein the connection coupling and the suction channel are arranged with respect to the suction connection flange in such a way that, with the suction connection flange mounted in the region of the opening of the wastewater tank, the suction channel extends into the wastewater tank and the connection coupling is arranged outside the wastewater tank, - a suction pump having a connection line which can be connected to the connection coupling in a fluid-tight manner, and - a pump control unit which is signal-connected to the suction pump for controlling the latter, and - a flushing channel (1043, 10143, 10245, 10345, 10445) which extends from a flushing connection flange, which is designed for fastening in the region of an opening of the wastewater tank to a flushing opening, - the pump control unit being designed to control a suction operation in such a way that o a suction operation of wastewater from the wastewater tank is carried out by means of the suction pump through the suction channel, the connecting line and the suction pump, and o a flushing process of the waste water tank is carried out through the flushing channel, characterized in that the suction pump is configured as a suction and flushing pump, and the pump control unit is configured to control the suction pump such that - in a first step, a suction process of waste water from the waste water tank through the suction channel and the connecting line takes place, - in a second step, the direction of delivery of the suction pump is reversed and a flushing process of the waste water tank through the flushing channel takes place, and - in a third step, the direction of delivery of the suction pump is reversed again and a suction operation is performed from the wastewater tank through the suction channel and the connecting pipe. - a suction channel (1043, 10143, 10243, 10443) extending from a suction connection flange formed for attachment in the region of an opening of the wastewater tank to a suction opening, - a connection coupling extending from the suction connection flange, wherein the connection coupling and the suction channel are arranged with respect to the suction connection flange in such a way that, with the suction connection flange mounted in the region of the opening of the wastewater tank, the suction channel extends into the wastewater tank and the connection coupling is arranged outside the wastewater tank, - a suction pump having a connection line which can be connected to the connection coupling in a fluid-tight manner, and - a pump control unit which is signal-connected to the suction pump for controlling the latter, and - a flushing channel (1043, 10143, 10245, 10345, 10445) which extends from a flushing connection flange, which is designed for fastening in the region of an opening of the wastewater tank to a flushing opening, - the pump control unit being designed to control a suction operation in such a way that o a suction operation of wastewater from the wastewater tank is carried out by means of the suction pump through the suction channel, the connecting line and the suction pump, and o a flushing process of the waste water tank is carried out through the flushing channel, characterized in that the suction pump is configured as a suction and flushing pump, and the pump control unit is configured to control the suction pump such that o a suction operation of wastewater from the wastewater tank is carried out by means of the suction pump through the suction channel, the connecting line and the suction pump, and o a flushing process of the waste water tank is carried out through the flushing channel, - in a first step, a suction process of waste water from the waste water tank through the suction channel and the connecting line takes place, - in a second step, the direction of delivery of the suction pump is reversed and a flushing process of the waste water tank through the flushing channel takes place, and - in a third step, the direction of delivery of the suction pump is reversed again and a suction operation is performed from the wastewater tank through the suction channel and the connecting pipe.