Section R. 325.3331 - Sewer design and installationRule 31.
(1) A sanitary sewer system shall be designed on the basis of an average daily flow of sewage of not less than 200 gallons per mobile home site per day.(2) A sanitary sewer shall have sufficient capacity to accommodate the maximum hourly sewage flow from the portion of the mobile home park or seasonal mobile home park being served and shall not be less than 4 inches in diameter.(3) A sanitary sewer shall be installed at a sufficient depth to prevent freezing and at a sufficient slope to maintain a velocity of 2 feet per second at design flow. The following minimum slopes shall be provided, although greater slopes are preferred where possible: | Sewer Size | Minimum Slope in Feet/100 Feet |
| 4 inch......................................... | 1.20 |
| 6 inch......................................... | 0.60 |
| 8 inch......................................... | 0.40 |
| 10 inch....................................... | 0.28 |
| 12 inch....................................... | 0.22 |
| 14 inch....................................... | 0.17 |
(4) A sanitary sewer shall be installed with straight alignment between manholes.(5) A manhole shall be installed at the end of each sewer line, at all changes in grade, size, or alignment, at all intersections, and at distances of not more than 400 feet along sewers. A drop pipe shall be provided for a sanitary sewer entering a manhole at an elevation 24 inches or more above the manhole invert. A cleanout may be substituted for a manhole at the end of a lateral not more than 150 feet in length. The flow channel through a manhole shall conform in slope and shape to that of the sanitary sewers.(6) A sanitary sewer shall be designed to prevent damage from superimposed loads. Proper allowance for loads on the sanitary sewer shall consider the width and depth of trench. When standard strength sewer pipe is not sufficient, extra strength pipe or special construction technique shall be used.(7) Leakage tests shall be specified by the engineer for sewer construction. Leakage outward or inward shall not exceed 200 gallons per inch of pipe diameter per mile per day.(8) There shall be no connection between a mobile home park or seasonal mobile home park water system and a sanitary sewer. A sanitary sewer or individual sewer service line shall not be laid within 10 feet horizontally of a waterline.(9) Where a sanitary sewer line crosses a waterline, there shall be a minimum of 12 inches of clear vertical isolation distance between the two. Where conditions require less vertical isolation, the sanitary sewer line shall be encased in concrete for 5 feet each side of the crossing. One full length of waterline shall be centered over the sanitary sewer crossing.(10) A mobile home sanitary sewer service connection shall incorporate a p-trap installed at a sufficient depth to prevent freezing. The p-trap and riser pipe shall be constructed of cast iron or schedule 40 plastic pipe. The riser shall terminate not less than 4 inches above final grade and shall be located not closer than 5 feet from a water service riser. A riser shall be securely capped when not in use.(11) A mobile home park or seasonal mobile home park shall be served by a common sanitary sewer system.(12) A site in a mobile home park or seasonal mobile home park shall be provided with an individual sewer connection.Mich. Admin. Code R. 325.3331