Run the house sewer in a straight line and avoid bends whenever possible. Slight changes in direction may be made with one-sixteenth or one-eighth bend fittings. For sharper changes of direction a manhole or distribution box may be used. Changes in direction of more than 45 are not recommended unless a manhole is provided. Clean-outs are desirable within 5 feet of the septic tank where tanks are placed more than 20 feet from the building and the sewer line is not buried deeper than 4 feet. Establishing Line and Grade The trench for laying the sewer is usually dug after the septic-tank excavation has been completed and the elevation of the tank inlet determined. A simple method of setting guides for the excavation is illustrated in figure 2. Digging the Trench Start digging the trench at the tank end, so that rain or seepage will have an outlet. Rounding the bottom of the trench to the shape of the pipe and hollowing out basins for the "bell" ends allows the pipe to rest firmly throughout its full length, permits full calking of joints, and relieves the strain on them. Laying the Pipe Begin laying the pipe at the tank with the bell end uphill. Joints in clay-tile pipe are commonly made with portland cement mortar or grout. Where root-proof joints are essential, sulfur-sand compounds may be used or copper rings provided and used with cement-mortar joints. Asphalt-mastic compounds, however, are more satisfactory. For cast-iron soil pipe, lead is the standard joint material. After the hub is pushed into the bell, oakum (or old hemp rope) is packed with a calking iron or a piece of wood (fig. 3, _A_.) solidly and evenly in the joint to a depth of about half an inch to center the hub end in the bell and to keep the joint filler from getting inside the pipe. Oil, grease, or dirt on the joint surfaces should be removed, as it will prevent joint material from sticking. Figure 3 shows the different jointing methods. [Illustration: Figure 2.--Establishing grade for sewer. _A_, 2- by 4-inch stakes are set each side of the trench at convenient distances _a_, _b_, _c_, and _d_. Then a board is nailed horizontally on the stakes at _d_ at a convenient height above the bottom of the trench, that is, the bottom of the sewer leaving the house. A board is nailed likewise to the stakes at a the same height above the inlet to the tank that _d_ is above the bottom of the trench. Similarly, boards are set at _b_ and _c_ by sighting from _a_ to _d_ so the tops of the intermediate boards will be in line. _B_, The exact grade of the sewer is obtained by measuring from the grade cord with the 1- by 1-inch stick, shown in detail. The length of the stick must equal the height of the board above sewer at _d_.] Bituminous, sulfur-sand, lead, and other commercial joint compounds are poured while hot into the joint from a ladle (fig. 3, _F_), and when the work is well done they form a joint that is practically root-proof. They are more expensive than cement mortar.