100. "Dead Ends" in the distribution mains should be avoided as far as possible. If such "dead ends" exist, they shall be flushed not less than each ninety (90) days or more if conditions require. To insure compliance with this requirement, all "dead ends" or mains of four (4) inches in size or larger shall be equipped with hydrants or blow-off valves. Records shall be kept of all flushing of mains showing the date, place and duration of flushing.