The soil-pipe must be well supported along the cellar wall on brackets or hung from the floor joists by short pieces of chain or band iron. Special care must be taken to support the pipe at the elbow, where it turns upward, since a length of thirty feet of this pipe, weighing three hundred pounds, has to be provided for. It is a good practice to build a brick pier from the cellar bottom up to and around the elbow to support it firmly in the masonry. The joints in this drainpipe should be made with lead, ramming some oakum into the joints first and then pouring in enough lead melted to the right degree to provide an inch depth of joint. After the lead cools, it must be expanded or calked by driving the calking tool hard against it. To prevent rain finding its way between the soil-pipe and the roof, a piece of lead is generally wrapped around the soil-pipe for a distance of twelve inches or so above the roof, and then a flat piece of lead extending out under the shingles is slipped over and soldered fast to the other lead piece. The fixtures are connected to the iron pipe usually by lead pipe, the lead pipe being first wiped onto a brass ferrule, the ferrule being leaded into the Y branch. These Y branches are usually two inches in diameter and the lead pipe usually one and one quarter inches. Between the soil-pipe and the fixtures a trap must be provided with a water-seal of about an inch. _Trap-vents._ In city plumbing it is customary to vent traps; that is, to carry another system of pipes from the top of the trap nearest the fixture up to and through the roof. On most roofs, where modern plumbing has been installed, are seen two pipes projecting, one the soil-pipe and the other the vent-pipe, indicating the location of a bath-room below (see Fig. 61). In a single house, however, and particularly in view of experiments made recently on the subject of trap siphonage, these trap-vents seem hardly necessary. They were formerly insisted upon because of the feeling that by the passage of a large amount of water down the soil-pipe, sufficient suction might be induced to draw out the water from some small trap on the way, thereby opening a passage for sewer gas into the room. Experiments have shown that it is practically impossible to draw off the water from a trap in this way, and that the system of vent-pipes does little more than add to the cost. The traps themselves, however, are essential, and great care should be taken to see that each trap is in place and has a seal of the depth already mentioned. The best trap to use in any fixture is the simplest, and a plain S trap answers every purpose. It is always wise to have a clean-out at the bottom of the trap; that is, a small opening which can be closed with a screw plug, so that when the trap becomes clogged, it can be easily opened and cleaned (see Fig. 62). [Illustration: FIG. 62.--A trap.] _Water-closets._