The house sewer may be vitrified salt-glazed sewer pipe, concrete pipe, or cast-iron soil pipe. The latter, with poured and calked lead joints makes a permanently water-tight and root-proof sewer, which always should be used where the vicinity of a well must be passed; 4, 5, or 6-inch pipe may be used, depending mainly on the fall and in less degree on the quantity of sewage discharged. As a measure of economy the 4-inch size is favored for iron pipe. If vitrified pipe is used, either the 5 or 6 inch size is preferable, as these sizes are made straighter than the 4-inch size and are less liable to obstruction. Of the two the 5-inch size is preferable. The fall in 100 feet should never be less than 2 feet for 4-inch size, 1-1/2 feet for 5-inch size, 1 foot for 6-inch size. Figure 21 shows methods of making good joints. _A_, _B_, _C_, _D_, _E_, _F_, and _G_ are ordinary sewer pipe joints; _H_, is cast-iron soil pipe. [Illustration: Fig. 21.--How to make good joints. See text for directions and specifications.] _A_ shows the use of a yarning iron to pack a small strand of jute into the joint space, thus centering the pipes and preventing the joint filler running inside. The joint surfaces should be free of dirt and oil. The jute is cut in lengths to go around the pipe; a small strand is soaked in neat Portland cement grout, then twisted and wrapped around the small end of the pipe to be pushed into the hub of the last pipe laid. After the pipe is pushed home the jute is packed evenly to a depth of not over 1/2 inch, leaving about 1-1/2 inches for the joint filler. Old hemp rope or oakum dipped in liquid cement or paper may be used in place of jute, and the packing may be done with a thin file or piece of wood. _B_ shows the use of a rubber mitten or glove to force Portland cement mortar into the joint space. The mortar should be thoroughly and freshly mixed in the proportion of one volume of cement to one volume of clean sand and should be pressed and tamped to fill the joint completely. _C_ shows a section of finished joint. The fresh mortar should not be loosened or disturbed when laying the next pipe. _D_ shows method of pouring a joint with grout, which is quicker, cheaper, and better than using a rubber mitten. A flexible sheet-metal form or mold, oiled to prevent the grout sticking, is clamped tightly around the joint and is completely filled with grout consisting of equal parts of Portland cement and clean sand mixed dry, to which water is added to produce a creamy consistency. The pipes should not be disturbed and the form should not be removed for 24 hours. _E_ shows a section of grouted joint, well rounded out, strong, and tight.