All measurements, tests and analyses of the characteristics of waters and wastes to which reference is made in Sections 921.03, 921.04 and 921.07 shall be determined in accordance with Standard Methods for the Examination of Water and Sewage, and shall be determined at the control manhole provided for in Section 921.09, or upon suitable samples taken at such control manhole. In the event that no special manhole has been required, the control manhole shall be considered to be the nearest downstream manhole in the public sewer to the point at which the building sewer is connected.