Property subject to a lien for unpaid charges shall be sold for nonpayment of the same, and the proceeds of the sale shall be applied to pay the charges, after deducting costs, as is the case in the foreclosure of statutory liens. This foreclosure shall be by billing equity in the name of the city. The City Attorney is hereby authorized and directed to institute such proceedings in the name of the city in any court having jurisdiction over these matters against any property for which the bill has remained unpaid 30 days after a lien has been rendered.