18. (1) During the period of possession the authorised person may, subject to the provisions of this Act and the previous permission of the Collector, lease to any person for a period not extending beyond the period of possession any part of the banks of the tank or any right to take fruit from trees on, or other produce from, such banks or any right to rear and catch fish in the tank. (2) During the period any land of which possession is taken under section 6A or retaken under sub-section (3) of section 9B remains in the possession of an authorised person, such authorised person may, subject to the provisions of this Act and the previous permission of the Collector, lease to any person for a period not extending beyond the said period of possession any part of the said land or any right to take fruits from trees on, or other produce from such land. (3) Any sum due to the authorised person under any lease granted under this section shall be recoverable as a public demand. (4) All sums realised by the authorised person under any lease granted under this section shall be applied to the recovery of all costs incurred or likely to be incurred by the authorised person in carrying out the required improvements in the tank and by the Collector in carrying out the purposes of this Act in respect of the tank together with interest on such costs at the rate of ¹[fifteen] per centum per annum.