In the matter of safety, another question, which sometimes arises, is as to the danger from the plumbing apparatus where there is no sewer connection, or where it has to be made with a vault. The protection against sewer-gas is not from the sewer itself or the vault. It is entirely through protective apparatus in the house, and the manner of the connection with the vault or sewer.
One may consider the conditions of safety in plumbing apparatus under two general heads. First, as to the workmanship; second, as to design or plan of the apparatus. Nothing need be said as to the workmanship, excepting that the execution of the design, or the benefits to be derived from it, maybe entirely lost by defective workmanship. If the work is not properly executed, the design need not be considered. The result will be bad irrespective of the plan.
In considering the design of the apparatus, we will take into account the arrangement of the connections and fixtures. By the latter expression is meant the tub, the water-closet, the wash-bowl, and the sink, pump, etc. The connections which have to do with the safety of the apparatus are the traps and the waste pipes, or pipes which connect with the vault or sewer.
The main waste pipe inside the house is called the soil pipe. The smaller waste pipes from the fixtures connect with it. The soil pipe is of cast-iron, and usually four inches in diameter on the inside. It connects, full size, with the water-closet. Most other wastes are of lead, and are usually an inch and a half in diameter. In the soil and waste pipes there will naturally be the odors from the vaults and sewer, or from the foul matter which is in or passing through the pipes. Therefore, there must be means in each waste pipe, which connects a fixture with the main soil pipe, of preventing the passage of gas or air from it into the house. This is done by means of what is called a trap. The "S" trap is the commonest form; this name is given it from its shape, and illustrates its construction. If we take a letter S and turn it sideways we will get the form of such a trap. The right side or end would continue directly down toward the drain or soil pipe, and the left side would continue upward and connect with the fixture (see Fig. 6). The water from the fixture comes down and is forced upward through the bend by the pressure of water above, and from thence runs into the soil pipe or drain. Thus it will be seen that there is always a seal of water in the trap. There is always water in the trap as indicated by the depth of the bend of the S. There are hundreds of different forms of traps, but they are all constructed on the same principle; the idea being that the gas or air from the pipe would have to pass through the water in order to get into the house. The water in the trap is called the seal; it seals the passage of air as stated.