 in large diameter shallow holes dug in very stable soil. A ladder can be used when placing the upper courses. Before the liner reaches the height of the outlet pipe trench, lay the outlet pipe. Use a sand bedding in rocky soil. Otherwise the trench bottoms should be undisturbed earth. Be sure to seal the outlet pipe CONVENTIONAL WASTE DISPOSAL SYSTEMS Figure 5.15 Seepage pit liner construction. in the trench with clay, bentonite, cement, or other appropriate material SO that overflow will not run down the trench through the fill soil on the outside of the pipe (Figure 5.16). This could result in erosion of the pipe bed and the side of the pit. The outlet pipe should have a "T" fitting to prevent scum from reaching the down- stream pit. The inlet pipe should extend about 1 ft in from the liner and have an elbow on the end SO the flow of effluent will be directed downward and not strike and erode the opposite wall. Continue the liner construction, laying one course around the outlet pipe and one course above it. BE CAREFUL. Climbing out from under a 6-ft pile of concrete blocks in a 12-ft-deep pit could ruin your evening. A septic tank manufacturer may be willing to construct and deliver a cover for your seepage pit(s). If you are building your own cover, place reinforcing rod on 9-in. centers about 1 in. from the bottom of the cover. The rod should run in two directions and be wired at the intersections. The cover should be able to support more than 400 lb per square foot. Don't forget to cast an inspection port 9 in. in diameter into the cover. If inspecting the condition of the pit ONSITE Figure 5.16 Seepage pit outlet pipe. CONVENTIONAL WASTE DISPOSAL SYSTEMS 93 meant moving 3500 lb of concrete, not many inspections would be done. The port should be located over the end of the inlet pipe. The cover should be topped with about 12 in. of topsoil. Operation and Maintenance Proper seepage pits require no routine maintenance. Take the same care using the seepage pit as would be needed for conven- tional trenches. C