TABLE XXVI.

TABLE OF DIAMETERS OF HOUSE DRAINS.

With various grades, and for lots of different sizes, capable of discharging two

inches of rain per hour, when running three-fourths full.

Calculated by Robert Moore, C. E., St. Louis, Mo.

By an inspection of the Table, we see that a four-inch main house sewer is ample for any ordinary condition of service, even if roof water be admitted, the discharge of house sewage proper being only a very small percentage of the total volume. A smaller size than four inches is not to be recommended, however, for the reason that although it may be ample so far as estimated carrying capacity is concerned, it is more liable to obstruction. Under some circumstances it may be advisable to increase the size of the main drain to five or even six inches diameter, this limit should not be exceeded however. If one drain of this size is not ample it is better to increase the number.

In order to provide for ventilating the house drain it should be carried full size up through the roof. This venti

lation of house drains has been discussed in a previous chapter.

Grease Traps. The principal danger of stoppages in a house drain, properly laid, arises from the grease carried into it from the kitchen sink. This can be avoided by the use of a grease trap, placed under the sink. The objection to the use of a grease trap is that they need to be cleaned occasionally, and if not cleaned they get very foul.

Soil and Waste Pipes. Soil pipes, that is, pipes leading from water-closets, and waste pipes, that is, pipes leading from bath-tubs, wash stands, etc., may be either of iron or lead. Iron is the better material where it can be used, but lead is easier to fit and adjust where the connection between the fixture and the main drain is not direct. All iron pipes should be either enameled or coated inside and out with coal pitch varnish to give them a smooth surface and keep them from rusting. All junctions and changes in the direction of the pipe should be made by easy curves.

A very common fault is to make the upward extension of the soil pipe after it passes the highest fixture, of galvanized sheet iron, or even of tin. This is highly objectionable. It should be of heavy iron pipe throughout, and should extend well above the roof. It is a good plan to increase it in size above the roof to six inches, so as to lessen the danger of its being obstructed by the accumulation of frost. Ventilating cowls are of doubtful utility. A plain wire basket to prevent the introduction of articles liable to obstruct the pipes is better.

There is such a variety of branches, curves, off-sets, traps, etc., etc., now in the market, that there is no excuse for awkward and rough connections and interior projecting angles or pockets which will retain the solid portion of the sewage. The course of all pipes should be as direct as pos

sible, and the fixtures should be grouped so as to be reached as nearly as possible by upright soil pipes and short horizontal soil or waste pipes. Horizontal pipes cannot be carried any great distance along floors or ceilings or between joists, and preserve a proper inclination, for reasons which are obvious. It is customary to make waste pipes, particularly short ones, of lead, for the reason that it is much more easily manipulated than iron. The proper method of connecting the lead wastes to iron is by means of a thimble soldered to the lead pipe and caulked into a hub on the iron pipe.

Traps and Ventilation.-Every fixture should be provided with a trap, and since the object of the trap is to isolate the fouled interior surface of the waste pipe from the air of the room it is evident that the trap should be as close to the fixture as possible. Notwithstanding many efforts to introduce a trap whose seal cannot be broken by syphonage, and which will be self-cleansing, the plain-running trap of uniform bore is still in general use. This trap is liable to have its seal broken by syphonage, and to prevent this it is necessary to resort to a back air pipe, which is connected with the crown of the trap on the downward side, and passes to the roof independently of the ventilating pipe proper, or is connected with it above the highest fixture. This back air pipe should be of ample capacity to preserve the equilibrium of air pressure.

The system of back air vents is open to the following objections: It considerably complicates the system of piping, especially where fixtures are not closely grouped. There is a possibility of the pipes being fouled at their junction with the crown of the trap. It adds considerably to the expense.

Back air vents tend to increase the interior circulation of air considerably. This is beneficial, so far as purity of the interior of the pipes is concerned, but it also increases the