A method, wherein a multi-phase fluid is discharged with a total volume flow Q IN from at least one inlet structure into at least one settling tank, wherein the inlet energy is continuously optimized by adjusting an inlet opening of the inlet structure, with subsequent separation of phases of different weight into at least one return volume flow Q R and one effluent volume flow Qc each within the at least one settling tank, characterized in that up to the total volume flow Q IN in or at the inlet structure, by changing the position of the inflow boundaries of the inlet opening to each other or by at least temporarily dividing the inflow area into differently aligned partial areas, the total volume flow Q IN or at least a greater portion of the total volume flow Q IN as a partial volume flow Q II largely flows in direction of two to four o'clock at high load and at least a partial volume flow Q I flows in direction of five to eleven o'clock at low load out of the inlet structure, wherein three and nine o'clock define a horizontal axis, wherein the inflow boundaries are at least partially formed by a lower edge of a height-adjustable wall und by a height-adjustable elevation of a device (5a, 5b, 5c) and wherein the position of the inflow boundaries to each other or the division of the inflow area into differently aligned partial areas is changed by changing a vertical distance between the lower edge of the wall and an elevation of the device (5a, 5b, 5c) and/or moving the the elevation forming device (5a, 6b, 5c) and the in its height extension variable wall relative to a flow deflector (5c, P2, 7). wherein a multi-phase fluid is discharged with a total volume flow Q IN from at least one inlet structure into at least one settling tank, wherein the inlet energy is continuously optimized by adjusting an inlet opening of the inlet structure, with subsequent separation of phases of different weight into at least one return volume flow Q R and one effluent volume flow Qc each within the at least one settling tank, characterized in that up to the total volume flow Q IN in or at the inlet structure, by changing the position of the inflow boundaries of the inlet opening to each other or by at least temporarily dividing the inflow area into differently aligned partial areas, the total volume flow Q IN or at least a greater portion of the total volume flow Q IN as a partial volume flow Q II largely flows in direction of two to four o'clock at high load and at least a partial volume flow Q I flows in direction of five to eleven o'clock at low load out of the inlet structure, wherein three and nine o'clock define a horizontal axis, wherein the inflow boundaries are at least partially formed by a lower edge of a height-adjustable wall und by a height-adjustable elevation of a device (5a, 5b, 5c) and wherein the position of the inflow boundaries to each other or the division of the inflow area into differently aligned partial areas is changed by changing a vertical distance between the lower edge of the wall and an elevation of the device (5a, 5b, 5c) and/or moving the the elevation forming device (5a, 6b, 5c) and the in its height extension variable wall relative to a flow deflector (5c, P2, 7).