and the lower end at the level of the gravel fill in the absorption trench. If the soil is rocky, make the trench a couple of inches deeper and add sand as a bedding. The reason for this is that the slight movement of the pipe as water flows through it might, over time, cause the pipe to wear through where it contacts rocks. The slope of the connecting pipe should be no less than 0.25 in. per ft, and the pipe should be unperforated. Normally, unperfo- rated 4-in. PVC is used, although clay, bituminous fiber in some areas, polyethylene, and ABS pipe are acceptable pipe material. Connect one end of this pipe to the septic tank outlet and cut off the other end about 6 in. into the disposal trench. Now lay the perforated distribution pipe on top of the gravel and check for level. Slope should not exceed 3 in. per 100 ft. Connect the sections, holes down, and cap the far end. If clay pipe is used, cover the top half of the joints with a curved piece of galvanized sheet ONSITE WASTEWATER DISPOSAL Figure 5.11 Cemented gravel. metal (Figure 5.12). Gravel should be added to about 2 in. above the top of the pipe to protect the holes in the pipe from the backfill dirt. After the distribution pipe has been placed, multiple trenches have been connected by solid pipe, and gravel has been placed over the distribution pipe (don't worry about the gravel wearing holes in the perforated pipe), the layer of straw, untreated building paper, or synthetic fabric is placed over the gravel. If straw is used, 6 to 12 in. is recommended. In Atlantic coastal areas, marsh grass is often substi- tuted for straw. Newspaper and cardboard disappear too quickly. Next comes the backfill. You should notify the government inspector prior to this step if you need a sign-off. This notification may seem useless now, but if some future buyer of your house (and its masterpiece disposal system) should need a loan, the lending institution may insist on it having passed a prior inspection. Disre- Figure 5.12 Clay pipe joints. CONVENTIONAL WASTE DISPOSAL SYS