The policy statement regarding the maintenance of single-family residential service connections and lateral sewers, as contained in Sections 921.06(a), 921.11 and 921.12, are hereby modified, subject to the following rules:
(a) The City shall not clean, without charge, a lateral sewer more than twice in a twelve-month calendar period under Section 921.11 or 921.12.
(b) The City shall perform the services as set forth in subsection (a) hereof during the normal working hours of the Service Department.