Since the over-all efficiency of a drainage system depends on the last link, the run of pipe which ends the house system and connects with the main sewer or septic tank, we should understand the principles of its installation. Though the amateur plumber, with care and the proper tools and materials, could make this installation, it is not recommended that he try it. There is also the likelihood that local regulations will not permit the amateur to make actual connections with a municipal sewage system.
The safest and surest course would be to hire a competent like plumber and to watch as the installation is made to see that your planned layout is followed. This section will outline what are considered to be correct procedures and safeguards. It is hardly necessary to stress that judgment in the selection of materials will ensure an efficient lived sewer.
Cast iron pipe is usually suggested for house sewers, though vitrified clay piping has proved more than adequate in many cases. Platic could also be an option. Clay is less expensive initially, but it lacks the strength and wearing quality of iron. Clay pipe is also subject to weakening from tree-root pressure. However, in soil containing cinders or ashes, clay will not deteriorate as will iron.
House sewer to main sewer connection
Entry into the public sewer generally must be made under supervision of an inspector from the local health authority. Main sewers are usually about 10 feet under the street grade. The hole through which you intend to connect your house sewer is made well above the flow line of the main sewer so that your house sewer will connect at an angle of 45°. The main sewer wall is pierced carefully with a small hole at the desired point so that the wall of the main sewer will not crack or fall away. The small hole is then enlarged until it can admit your terminal pipe link.
Once this hole is the proper size, measure the main sewer's wall thickness and cut a sleeve of the pipe used to that size so that it can be cemented in place.
Place it so that its inner rim is flush with the interior sewer wall and so some of the sleeve extends up from the main sewer. This will prevent the sleeve and the first section of your house sewer from separating if there should be an underground shift of either, and it also avoids impeding the flow within the main sewer itself.
In most cases the entry of the house sewer into the main sewer is made in a long sweeping curve rather than at a sharp angle. The over-all angle should be the already suggested 45°
The pipe section is inserted into the sleeve, which has been firmly secured and cemented into place so that it will not shift.
This type of connection is made in the main sewers of either the concrete or brick type. If the main sewer is of vitrified clay, an entire section of it may be removed and replaced with a Y-fitted section, unless the main sewer is already supplied with Y fittings at regular intervals along the line.
Having determined the material from which the sewer will be made, and having made the proper main sewer connection, it is now time to lay the pipe to the house at a pitch which will permit proper discharge. The diameter of your house sewer pipe should be checked with local authorities. Generally it should be 4" diameter if iron or copper is used and 6" if clay pipe is selected.
To determine the pitch, you must know the lowest depth of the house sewer and the depth of the main sewer. Since these two points are to be connected, you must be sure your house sewer outlet is sufficiently higher than the other to insure a pitch that will enable waste water to drain out by gravity.
The generally accepted minimum pitch is 1/4" per foot. The pitch may exceed this figure over-all, but the best procedure is to let the house sewer have the minimum pitch from the main sewer connection to the curb; then add additional grade through the use of 1/8 bends until a height is reached sufficient to provide the 1/4-inch grade from that point to the house drain.
A 1/4"-grade is approximately the same as a rise, or fall, of 2 feet in a horizontal distance of 100 feet. You can dig the trench for the sewer at this pitch by the following method. Stretch a level line from the building at the point where the sewer will leave it to the point where the sewer will connect with the main or septic tank. Attach this line to a stake at either end to hold it above ground and use a spirit level to get it horizontal. Then lower the end of the line at the main the necessary distance to get the proper pitch.
For a horizontal run of 100 feet, lower it 2 feet; for a run of 50 feet, lower it I foot; for 25 feet, lower it 6"; and so on. Cut a measuring stick to a length equal to the distance from the level line, to the bottom of the drain where it leaves the building, and use this as a guide to the depth of the trench from the level line throughout its course.
The house sewer should be laid below frost depth.
Another point is to concider is the kind of soil in which the sewer pipe will be laid. If it is exceedingly sandy, it may be necessary to shore up the sides of the trench in which the pipe is to go. If it is overly wet, a wooden platform may be necessary to support the sewer. Clay soil should give little trouble as long as it is not permitted to cake into large pieces.
All connections along the run of the house sewer are made as described later on. When using any sort of metal piping, remember to make an allowance for expansion and contraction. This may be done with copper by putting an expansion turn in the piping or by making a gooseneck near the sewer connection. With iron pipe, an extra bend is fitted in or extra pipe is allowed.
Since copper expands more readily than iron, more allowance must be made when this metal is used. About 1 1/2" per hundred feet should be sufficient.