Having now considered the two fundamental subjects of traps and venting, the entire plumbing system will be considered, beginning at the point where the house sewer connects into the public sewer. Before proceeding with the subject, it will be well to define several terms, which are not always clearly understood.
By house drain is meant that portion of the horizontal drainage system into which all soil, waste, and drainage pipes discharge within the walls of the building which the drainage system serves. The house drain conveys the drainage to a point outside the foundation walls into the house sewer.
By house sewer, lateral or main drain, is meant that portion of the horizontal drainage system which extends from the house drain outside the foundation walls into the public sewer.
By house connection is meant that part of the house sewer which lies between the public sewer and the curb line.
By crock drain or sewer is meant any drain or sewer constructed of vitrified earthenware, hub and spigot pipe.
By tile drain is meant any drain constructed of hard-baked earthenware pipe, which is laid with open joints, and having no hub and spigot ends. Tile drain is a name often wrongly applied to the crock drain.
The house drain usually ends at a point 10 feet outside the foundation walls, and at this point enters the house sewer, which is generally constructed of vitrified earthenware pipe, although occasionally the cast-iron pipe of the house drain is continued to the public sewer. No earthenware pipe should be allowed inside the foundation walls of any building, on any part of the drainage system. All plumbing ordinances now make this prohibition. The reason for this is that owing to their nature, the cement joints used on this style of pipe are liable to break or crack, or the pipe itself to suffer like injury, in which event the sewage will leak out and produce conditions unsanitary in the extreme. Breaking of pipe and joints may often occur from various causes, such as settling of the ground, etc.
The house connection is a term not so definitely defined as might appear from the definition above.
In some cities the house connection continues only to the curb line, in others to the fence line, and occasionally to the house sewer at the foundation wall. In each case this part of the drainage system is usually under the care of the municipal authorities, and the plumber allowed to work on it only under certain conditions and restrictions. In many cities a regularly appointed sewer inspector inspects all work done on the house connection, and only those plumbers may perform this class of work who have the proper license and permit from the proper officials.
This chapter will have to do principally with the house sewer.
This part of the drainage system, as before stated, is generally of vitrified earthen pipe. Much care should be exercised in making the connection between the house sewer and the public sewer, as a serious fault at this point renders an otherwise perfect drainage system useless.
Fig. 68 will serve to show some of the points of importance that should be observed. In the first place the branch for the house sewer should enter the street sewer above the center at a point high enough to guard against the setting back of the contents of the street sewer into the house sewer at such time as the former is carrying its maximum amount of sewage. It can readily be seen that in the backing up of sewage into the house sewer there is danger of the latter being closed up with heavy matter from the street sewer.
In addition, a Y branch, pointing in the direction of flow in the street sewer, is preferable to a tee, inasmuch as there is less liability of the collecting of such materials as rags, paper, etc., about the entrance.
An eighth bend into the Y will bring the course of the house sewer at right angles to the street sewer. Sharp, abrupt bends should never be used on this part or in fact on any part of the drainage system. If necessary to make a turn of 90 degrees, it should be done by means of eighth or sixteenth bends rather than by the use of a quarter bend. Precautions should be taken that the Y branch, or any cement used in making the joint, may not project inside the street sewer and thus present projections upon which matter floating in the sewage may catch. The house sewer should be laid on a grade of not less than 1 foot in 100 feet, and more pitch is desirable when possible to secure it. The trench in which the house sewer or any other underground drain is laid, should have a uniform slope and on the bottom depressions should be made to receive the hubs of the pipe. Each length of pipe should be given a solid bearing throughout its length. The best foundation for the laying of the house sewer is a natural bed of earth, gravel, rock, or sand. If such a foundation is not attainable, concrete may be laid beneath the pipe as a support. Chestnut planking also makes a good foundation on which to lay the pipe. Whenever the ground is made, or filled in, or where there is possibility of the settling of the pipe, or danger from the roots of trees, from frost, etc., it is preferable to construct the house sewer of extra heavy cast-iron pipe. The earth about the pipe should always be well rammed.
Fig. 68. - Connection of House Sewer into Public Sewer.
Special care should be taken in the making of joints on this part of the work. In general this work is done by unskilled workmen, and the attention is not given to it that its importance should demand.
If the joints are unglazed they should first be wet, and the space between hub and spigot completely filled with Portland cement. This cement should be made of one part Portland cement and three parts of clean sand. In the use of pipe having glazed hub and spigot ends the hub should first be calked half full with oakum, and the remaining space filled with Portland cement. This method should also be followed in making the joint between the cast-iron house drain and the earthenware house sewer.
In the case of the last-named joint, if the house sewer is more than one size larger in diameter than the drain, an increaser or reducer should be used in making the connection.
After each cement joint is made and before starting on the next one, all mortar projecting from the inside of the joints should be cleaned off by the use of a swab.
The danger of leaving superfluous cement projecting into the drain may be seen from Fig. 69. Such projections present sharp, rough surfaces, against which various substances contained in the sewage passing through the pipe may collect.
Fig. 69. - Danger of Cement Projecting inside Drain Pipe.
It often happens that pipe of too large size is used for the house sewer. It is true that it is almost as serious a matter to use too large pipe for horizontal drains and sewers as to use too small pipe. If the pipe is of proper size the sewage flowing through it passes out more rapidly, and with greater scouring action than if running sluggishly at the bottom of a pipe of large diameter. Thus, in Fig. 70 it may readily be seen that as the waste in the smaller pipe more nearly fills it than the same amount of waste in the larger pipe, such scouring action must certainly be greater in the small pipe. The solid matter carried by the sewage in the larger pipe has greater opportunity of lodging on the surface of the pipe also. Therefore, if a 5-inch pipe will perform the work in an entirely satisfactory manner it is obviously unwise to use a larger size.
Fig. 70. - Flow of Drainage through Large and Small Pipes.
The great danger in the use of earthenware pipes is that they may crack or be broken or that the joints may not be tight, under which conditions the surrounding soil becomes polluted and earth works into the drain, as in Fig. 71, eventually causing stoppage and the backing up of the house sewage. For this reason an earthenware drain or sewer should not be laid less than 3 feet beneath the surface, or within 25 feet of any well or other source of water supply.
Fig. 71. - Settling and Breaking of Earthenware Pipes.
A restriction now laid down by nearly all plumbing ordinances is that no house sewer or drain shall receive sewage from any other house. In many cities two systems of sewers are now maintained, one for the disposal of house drainage, the other for surface water. Under these conditions the rain leaders should not be connected either into the house drain or sewer. Where there is no double sewage system, however, it is allowable to connect the rain leaders into the house sewer and often allowable to connect them into the house drain. When connected into the house sewer, each rain leader should be trapped, in order to prevent direct communication with the house and public sewers.
The main trap is sometimes placed on the house sewer, but it is better to locate it inside the foundation wall on the house drain, where it is more accessible, and often less susceptible to the action of frost.
Fig. 72. - The House Drain and Its Connections.