When a part of one cemetery district is transferred to another as provided by RCW 68.54.100 and 68.54.110, said part shall be relieved of all liability for any indebtedness of the district from which it is withdrawn. However, the acquiring district shall pay to the losing district that portion of the latter's indebtedness for which the transferred part was liable. This amount shall not exceed the proportion that the assessed valuation of the transferred part bears to the assessed valuation of the whole district from which said part is withdrawn. The adjustment of such indebtedness shall be based on the assessment for the year in which the transfer is made. The boards of commissioners of the districts involved in the said transfer and merger shall enter into a contract for the payment by the acquiring district of the above-referred to indebtedness under such terms as they deem proper, provided such contract shall not impair the security of existing creditors.