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• <br />LET <br />9. Distribution pipe used in trenches or beds for <br />gravity flow distribution shall be materials allowed <br />by the State Plumbing Code, and at least four inches <br />in diameter and constructed of sound and durable <br />material mot subject to corrosion or decay or to loss <br />of strength under -continuously wet conditions. <br />(a) Agricultural drain the shall be in 12 -inch <br />lengths and laid with 1/4 inch open joints'on <br />grade boards. All open joints shall be protected <br />on top by -strips of asphalt -treated building paper <br />at least ten inches long and three. to six inches <br />wide or by other acceptable means. <br />.(b) Perforated plastic pipe shall be laid with one <br />row of perforations on the•bottom. Perforations <br />shall be at least 1/2 inch in diameter and spaced <br />no farther than 36 inches apart. <br />(c) Other devices may be used to distribute sewage <br />tank effluent over the soil treatment area after <br />City approval. <br />10. The distribution pipes shall be laid level or on a <br />uniform slope away from the sewage tank of no more <br />than four.inches per 100 feet. <br />11. The distribution pipes in beds shall be uniformly <br />spaced no more than five feet apart and not less <br />than 30 inches from the side walls of the bed. <br />12. The filter material shall completely encase the <br />disposal pipes to a depth of at least one inch. <br />13. The filter material shall be covered with untreated <br />building paper or a two-inch layer of hay -or straw <br />or similar, approved permeable materials. <br />14: The trenches or beds shall be backfilled with the <br />excavated material and slightly crowned -above <br />finished.grade to allow for settling. The .backfill <br />shall not be compacted to a density greater than that <br />of the original soil. <br />15. The minimum depth of cover over the distribution pipes <br />shall be at least eight inches. <br />