The plumbing installation for the house itself begins with the laying of the house drain, which is the pipe that receives all waste and water discharged by the soil stacks and waste lines. This house drain is laid from a point just outside the building foundation wall where it connects to the house sewer, then through the wall, and either along or under the cellar floor to the point where connection with the soil stack is made. Before laying this drain, determine its overall length and how much pitch to give it so that it will drain as it should.
House drains are usually placed as soon as possible so the plumbers can work from the ground up as the building is being built. An underground drain is more economical and will not reduce headroom as a hanging drain would. Cast iron pipe is recommended for most drains, especially those placed underground, but as in the case of the house sewer, both copper and vitrified clay pipe have been used successfully.
The two major types of drains are the sanitary drain, which receives the sanitary and domestic wastes, and the storm drain, which receives only that waste which is drawn off when it rains. Often the discharges from both these drains are kept separate and are drawn off to different terminuses--the sanitary drain to the main sewer or septic tank, the storm drain to a nearby lake, river, or other natural drainage area. However, in many cases, both soil and storm stacks fall into a common or combination drain and flow together into the sewage system.
The house drain
Like the sewer, the house drain must be of sufficient size to service the pipes draining into it. A 4" iron or copper pipe is commonly chosen, but many plumbers believe a 5" or 6" drain is preferable. Much depends on whether the drain is serving as a combination for both soil and storm stacks. If it does, the diameter should be based on the maximum discharge of both stacks and the surface area drained by the storm stack. If it drains only the waste stack, diameter is based on the discharge of all fixtures emptying into it. If it drains one or more water closets, 4" pipe should be used.
A 1/4"-per-foot pitch is also used for the house drain, except in those cases where such a grade would bring the house drain below the level of the house sewer connection. A steeper grade is possible but will not give the self-scouring action that the minimum grade will. Any fixtures below the level of the house sewer line must have a drainage system that pumps wastes up into the sewer line.
The house drain, like the house sewer, should be beyond the reach of frost. House drains sometimes become clogged, so it is necessary to provide clean-outs at accessible points no less than 50 feet apart. A clean-out nothing more than a capped section of pipe run into the drain with a Y fitting that extends above the pipe. The cap, usually of the screw-thread type, should be in an accessible area so that it may be readily removed to give access to the main run.
In making the actual installation, begin at the outside connection with the house sewer and work into the house toward the soil stacks. After making this connection and coming through either the cellar wall or floor, place a clean-out just inside the wall. Other clean-outs should be placed at the base of all soil stacks, floor drains, or direct runs from fixtures. To avoid impeding the flow of waste, all changes of direction should be made with fittings giving a long or sweeping radius, rather than a sharp one.
After having completed all the prior planning, where the drain is to run, what branches will be needed, location of clean-outs, size and kind of pipe to be used, and the pitch, we are ready to lay the pipe. First, the trench in which the pipe will rest is dug to the desired depth and graded. If the drain requires extra protection, such as shoring or base boards, these should be put in place also. Trenches should be about 12" deep for iron, and 18" deep for clay pipe.
The pipe itself may be laid section by section, but a better procedure, especially in those runs containing a clean-out, is to fit three or four sections together outside of the trench and then set this longer section in at one time. Sections having Y fittings or change-of-direction fittings can also be prepared in this manner and then placed so that the fittings face in the proper direction.
Support is particularly needed at all points where stacks are connected with the drain, as the greatest strain the drain will be subjected to will occur at these junctions because the weight of the entire stack is upon them.In laying the drain pipe, it is considered best to run the drain from the outside connection with the sewer directly to the farthest point, with all fittings for branches in the proper place and facing in the proper direction. The need for precise planning of branches is therefore quite evident. Any right-angle turns should be made by a Y fitting and a 1/8 bend rather than by the sharper T fittings.
Since you know beforehand the number and position of soil and waste stacks, it is good practice to run the house drain on a line which roughly divides them equally by location and volume of discharge. Too great inequality on one side may cause a sudden discharge to run up into branches on the other side.