[Figure 30] shows two other methods of controlling the flow on steep slopes and diverting proper proportions to the several lateral distributors laid along the contour of the field. This work can not be effected properly with T or Y branches; the flow tends to shoot straight ahead, comparatively little escaping laterally. To overcome this difficulty recourse is had to diverting boxes, of which two types are shown in [Figure 30]. These boxes involve expense, but permit inspection and division of the flow according to the needs. They may be built of brick, stone, concrete, or even wood.
Type 1 consists of a single box, into which all the lateral distributors head. It will be noted that the laterals enter at slightly different elevations, the two opposite the inlet sewer being the highest, the next two slightly lower, and the next two the lowest. This staggering of the outlets, in a measure, offsets the tendency of the flow to shoot across and escape by the most direct route.
Fig. 28.—Four methods of protecting open joints in distribution lines—an all-important work. Sketches show cross-section and longitudinal views; the depth from the surface of the ground to the top of the tile is about 10 inches
1. A, Subsoiled ground; B, 3 or 4 inch drain tile; C, strip of tarred paper about 6 inches wide and extending three-fourths the distance around the tile, allowing sewage to escape at the bottom; D, coarse sand, gravel, broken stone or brick, slag, cinders, or coke, the coarsest material placed around the tile (where the ground is naturally very porous and well drained, special filling in the trench may be omitted); E, natural soil.
2. Drain tile covered with a board laid flat, leaving the entire joint open.
3. Drain tile laid in stoneware gutter pieces and the joint covered with stoneware caps; gutter and cap pieces are inexpensive commercial products; their radius is longer than that of the outside of the tile, thus leaving open most of the joint space; the gutter aids in keeping the tile in line.
4. Vitrified sewer pipe with hubs facing downhill; the spigot end should be centered in the hub with a few small chinks or wedges.
Fig. 29.—-Close soils should be deeply subsoiled and underdrained. Porous, well-drained, air-filled soil is absolutely necessary. A, Subsoiled ground; B, 3 or 4 inch distribution tile; C, depth variable with the climate, 1¼ to 3½ feet; D, 4-inch underdrain; E, depth such as would prepare land for good crop production, generally 3½ to 4 feet; F, stone or other coarse material; G, gravel grading upward to coarse sand; H, loose soil