Such funds on deposit shall not bear interest and shall be refundable, either at the option of the City of Phoenix or the owner, provided said funds have not already been applied on the satisfaction of the aforesaid assessment. The City of Phoenix shall not add any of its own monies on the satisfaction of such assessment and shall not accept any such funds on deposit unless a prior satisfactory written agreement has been entered into, the form of which agreement shall be adopted by the City Manager and/or his nominee, which agreement shall include, among other things, a provision absolving the City from any and all liability in the event sufficient funds are not on deposit to satisfy any assessment installment. (Ord. No. G-804, § 1)