Each borough shall retain and pay any debt or liability which exists immediately prior to the formation of the united city. The title to and revenue from all property of each borough is transferred to the united city, except so much thereof as may be necessary to pay any debt or liability which existed immediately prior to the formation of the united city. With respect to the property transferred, the united city may consolidate, interconnect and manage any municipally owned facility, utility, water, sewerage or sewerage disposal system, provided that such consolidation, interconnection or management does not adversely affect the rights of any existing bond holders. If the bonds of any municipality, before it becomes a borough, have been registered with the State Auditor of Public Accounts, as required by law, the county clerk of the county in which the borough is located shall certify forthwith the fact of the formation of the union to the Auditor. The Auditor shall continue to certify any existing tax rate, and the county clerk shall continue to extend such existing tax rate upon the taxable property of the particular borough alone until the payment of the principal or interest of the bonds of the borough is complete. Nothing in this section shall be construed to prevent the united city from incurring indebtedness for the city as a whole after its formation.