Each county and city treasurer shall proceed promptly to collect all individual and fiduciary income taxes for the taxable year that have been assessed by the commissioner of the revenue and remain unpaid after the time fixed by law for payment and shall continue his efforts so to collect until the close of the then current calendar year. The collection of such taxes shall be enforced by legal process, as provided in § 58.1-3919, and all remedies available to the treasurer for the collection of other taxes shall apply to the collection of individual and fiduciary income taxes. Forms of necessary tax bills and receipts shall be prescribed by the Department. Within thirty-one days after the close of such calendar year, the treasurer shall transmit to the Department in such form as the Department may prescribe such information and data as may be required by such Department with respect to all assessments made by the commissioner of the revenue during such calendar year as the treasurer was unable to collect. The Department, upon receiving and examining the same, shall certify to the Comptroller the necessary information to enable the Comptroller to give such treasurer proper credit on the Comptroller’s books for all unpaid items, and such treasurer shall not receive any of such taxes after he has transmitted such information and data to the Department, but the same shall be paid directly into the state treasury.