An exterior drop pipe should be provided for a sewer entering a manhole at an elevation of twenty-four inches or more above the manhole invert, as provided in the rules and regulations of the Illinois Sanitary Water Board.  The minimum diameter of a drop manhole shall be forty-eight inches.  The diameter of the drop pipe shall preferably be larger than, or of the same diameter as, the entering sewer.  The diameter of the drop pipe shall not be smaller than the diameter of the entering sewer by more than two nominal diameters (e.g. for twelve-inch, fifteen-inch and eighteen-inch entering sewer, the drip shall be eight inches, ten inches, and twelve inches, respectively), provided that the minimum diameter of the drip pipe shall not be less than eight inches.  If a smaller drop is desired, design calculations and configurations shall be submitted for review and approval.
(Ord. 1975-15.  Passed 11-10-75.)