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4 — <br /> Hydraulic cleanouts are normally considered superior to manholes for pipes <br /> conveying settled sewage; however, manholes may be necessary at the junctions of. <br /> two or more small diameter gravity sewer lines. Specification of watertight man® <br /> hole covers at such locations is desirable because problems with grit have been <br /> experienced with the use of conventional covers. Manholes should be located where <br /> they will be least susceptible to damage from snowplowing. <br /> Gases generated in the septic tank under anaerobic conditions may be toxic; <br /> consequently, the creation of turbulence, which enhances the release of gases from <br /> the septic tank effluent, should be avoided through proper design practices. Accord— <br /> inglye the use of drop inlet manholes is discouraged. <br /> In designing small diameter septic tank effluent piping systems, additional <br /> consideration should be given to protect against freeze—ups due to construction <br /> at ground depths susceptible to frost penetration. This is necessary because <br /> piping from septic tank outlets is normally shallower than that of conventional <br /> gravity building sewers, which is often at or below the basement floor level. <br /> Only in cases where special circumstances exist and sound engineering prac— <br /> tices allow, will deviations from the foregoing criteria be considered. <br /> Effort should be made to establish septic tank maintenance districts or cleaning <br /> procedures in conjunction with the facility planning and design phases, recognizing <br /> that the key to successful operation of these systems is retention of solids in the, <br /> septic tank. Sewer use ordinances and/or local health codes should, therefore, <br /> include adequate provisions to ensure proper operation, use, connection to, and <br /> construction of such small diameter sewers. <br /> APPROVED FOR DISTRIBUTICN: <br /> William C. LaRow, P.E. <br /> Director Director <br /> DIVISION OF CONSTFUCTION MANAGEMEKT DIVISION OF WATER <br /> Technical Information Pamphlets (TIP's) will be issued from time to time. It <br /> is suggested that interested parties maintain them in loose—leaf binders for <br /> continued reference. <br />