Measure the cistern. If it is round, take measurements of the depth and diameter. If it is rectangular, take measurements for the length, width and depth. Convert fractions to decimals and plug the figures into the following calculation to determine how much fill you need:
Round: Volume in yards cubed = [(diameter x 3.14 / 4) x depth] / 27
Rectangular: Volume in yards cubed = (length x width x depth) / 27
Remove all pipes from the cistern and plug exposed connections. Pump any remaining water using a cistern water pump.
Dig a trench with a backhoe along one side of the cistern. Cave in one wall of the cistern with the backhoe, all the way down to the floor. This ensures that any water entering the cistern in the future will automatically leak out.
Fill the trench and cistern with the soil dug from the trench; add other soil if necessary. Pack the soil as you fill the cistern using the backhoe. Fill the final 12 inches with top soil, dumping a little more than is necessary to accommodate settling of the soil.
Plant vegetation similar to adjacent areas in the newly filled space so it blends in with its surroundings.