For the purpose of refunding, extending, and unifying the whole or any part of any valid outstanding bonded indebtedness payable from the revenues of a sewerage system, any reorganized common sewer district may issue refunding bonds not exceeding in amount the principal of the outstanding indebtedness to be refunded and the accrued interest to the date of the refunding bonds. The board of trustees of the reorganized common sewer district shall provide for the payment of interest which shall not exceed the same rate and the principal of the refunding bonds in the same manner and from the same source as was provided for the payment of interest on and principal of the bonds to be refunded.