_A._—Sewer; _B._—Intercepting trap; _C._—Cleaning eye for pipes between chamber and sewer; _D._—Inspection chamber; _E._—Inlet ventilator; _F._—Gully-trap for forecourt; _G._—Air-bricks for ventilation under floors; _H._—Damp-proof course[8]; _I._—Concrete 6” thick over site of house; _J._—Drain, fall 1 in 24, imbedded in concrete; _K._—Soil-pipe carried up full size above eaves; _L._—Upstairs w.c.; _M._—Gully-trap receiving water from _N_ scullery-sink, _O_ bath and _P_ rain-water stack-pipe; _S._—Ventilating pipe at upper end of drain; _T._—Pipes leading to same. ] =The soil pipe= is the vertical pipe carrying the contents of the water-closets in the drain. It must be distinguished from the drain, which is chiefly, if not entirely, underground. The exact position of the soil-pipe and its relation to the drain can be seen in Fig. 28 and 29, which should be carefully studied. The soil-pipe should be made of drawn lead without seam, of uniform thickness throughout, and of at least 7 lbs. or better 8 lbs. weight per superficial foot. Any joints in the lead pipe should be of the kind known as “wiped,” not a “slip” joint. The outside of a wiped joint is shewn in Fig. 30B. Iron pipes if used must be 3∕16 inch thick, and have sockets sufficiently wide and strong to permit of the joints being caulked with molten _i.e._ “blue” lead, in the same way as water-mains are laid. The soil-pipe should be throughout its course under observation. It should not be built into a wall, where it might be accidentally pierced by nails, nor within the house, allowing foul gases to escape from weak points in the joints. It should be carried through the wall of the house immediately beyond the closet trap. The soil-pipe should not be more than four inches in diameter. It should be continued from its highest point at the junction with the closet-trap above the roof by a pipe of the same diameter, with its end wide open (Fig. 29 K). This _ventilation of the soil-pipe_ is essential (_a_) to prevent the entry of foul effluvia into the house, especially when the water in the closet-trap is dried up; (_b_) to prevent unsyphoning of the upper by the lower water-closets in a house. (On this point see p. 172). [Illustration: FIG. 30. A.—SECTION SHOWING A GOOD METHOD OF CONNECTING SOIL-PIPE TO DRAIN BY BRASS THIMBLE. B.—OUTER VIEW, SHOWING BRASS THIMBLE WIPED ON TO SOIL PIPE.] The upper end of the ventilating pipe should be made to open remote from any window. It may have a cowl attached to it, but it is doubtful if this materially aids the aspiration of foul gases. It is wise to cap the upper end of the ventilating shaft with a dome of large meshed wire-netting to prevent birds building their nests in it.