Whenever any special assessment or special assessment taxes are levied upon land or real property by any city, county, district or other public corporation, officer, or body, and the same are to be collected by the county or any county officer, whether acting as a county officer or as an ex officio officer of the city, district, public corporation, officer, or body, there shall be added to the amount of the special assessment or special assessment tax an amount fixed by agreement between the county and city, district, public corporation, officer, or body for each special assessment or special assessment tax to be collected. An equal part of such charge shall be collected with each installment of such special assessment or special assessment tax and shall be deducted by the county officer collecting the tax and by him be paid into the general fund of the county.