The next point for consideration is the house sewer and its branch pipes from this disconnecting trap to the various positions required to receive the solid and liquid matter from the house appliances; and it may be mentioned at once that too much care cannot be bestowed upon the laying of these conduits, as leakages from faulty joints or imperfect pipes will percolate through the soil to a great distance, and may eventually locate themselves, and the evils arising therefrom, beneath the dwelling, to the detriment of the health of the inhabitants.
These drain pipes are generally of glazed stoneware, about 2 feet in length; but of late years many schemes have been carried out in strong cast iron, having its surface coated with glass enamel, or with Dr. Angus Smith's solution of hot coal tar, oil and resin, or other non-corrosive material, the advantage claimed being a better connection, that will stand a high pressure, powerful flushing, and a reduced number of joints, on account of the iron pipes being in 9-feet lengths, as compared with 2-feet lengths in stoneware pipes. Stoneware pipes, however, have this strong point in their favour - that they are made of an imperishable substance, which iron is not; and, moreover, iron pipes, properly treated, cost nearly double the price of stoneware pipes, bedded in concrete as an additional precaution. These pipes should be egg-shaped, so that a greater hydraulic depth can be obtained for small flushes, to enable them the better to allow the water to carry any solid matter with them, scouring out the drain completely, and also to increase the velocity of the flow.
This reduction of the width of the channel, with its corresponding increase of depth, is attained by the use of pipes similar to Figs. 993 and 994, the latter of which - on account of its loose lapped cover - reduces to a minimum the risk of obstruction formed by the squeezing up of the cement used in bedding the bottom joint. Both these pipes have another advantage, in that they do not require so much water to flush them.
They should be laid perfectly straight, on a solid foundation of concrete, and to a gradual fall from point to point (of, say, 2 inches in 10 feet), according to the size of the pipe - a simple method for calculating the fall of drains and sewers being to multiply the diameter by 10 and call it feet, the result being the length of pipe that should have 1-foot fall - e.g., 4 inches X 10 = 40 feet, or 1 foot in 40, the required fall for 4-inch pipes.
It should be borne in mind that this is the minimum rate of fall that is advisable and likely to answer its purpose, and a greater fall should be the aim of the sanitarian.
If the fall is not sufficient, the contents are likely to silt up and choke the drain; while if too much fall is given, the liquid matter will run too quickly away from the solid, which would thus accumulate, and also choke up the pipes.
The inside circumference of the pipes should be in perfect alignment when fixed together, and all joints should be made thoroughly sound; those in stoneware where patent joints are not employed being made of tarred spun yarn and cement, the cement being mixed with clean sand, in the proportion of about 1 and 1 (otherwise the expansion in setting is liable to crack the sockets), and care should be taken that no cement or projection is left on the joint in the inside of the pipe; while in the case of cast-iron pipes the joints are made by lead being well caulked into the sockets, so that the pipe joints are strong enough to stand the smoke, peppermint, or water-pressure tests, the latter being the best, consisting of blocking up the drain at the outfall and filling with water, which will be retained at a regular level if all is secure. All drains in close proximity to dwelling-houses should stand the water test, otherwise a stoppage in the pipes, causing them to fill up at any time, would force the joints, and cause leakages that may never be discovered.
The other tests are applied by forcing fumes of smoke or peppermint into the pipes; and these fumes, if the system is secure and a good job, should not escape at any place (so that the odour should be perceptible) except at the top of the soil or vent pipes.
Of the patent systems of jointing stoneware socketed pipes one of the most important is Doulton's self-adjusting joint, Fig. 995, which consists of concave and convex rims made of hard, imperishable material, and which are attached to and incorporated with the material of the spigot and faucet ends of the pipes, the spigot end fitting into the socket or faucet, both having previously been smeared over with an oily mixture, so that a turn of the pipe will cause a close-tilting joint to be made between the hard, true surfaces of the rims. Another form of oint is the Albion "Paragon," similar to Fig. 996, which explains itself, the clay or cement being forced by the insertion of the spigot to make a water-tight joint. A still later and more improved kind is known as "Sykes" patent joint, as Fig. 997, from which it will be gathered that, being a screwed thread, so to speak, to be twisted into position, it can be made by the ordinary workman, the jointing material being said to be water-tight and imperishable, and yet flexible - the quality which has been a long while sought, as it is impracticable to make a perfectly rigid joint water-tight, owing to settlements in the ground.
Another similar joint is illustrated by Fig. 998, which also allows of flexibility in the connection - a point which, together with the fact that perfect alignment is rendered the more certain, gives a great deal of preference to patent jointed pipes over the ordinary rigid cement and yarn; this latter being most uncertain, owing to unequal settlements of the ground.
Further, the mere filling-in of the soil in deep drains often breaks the joint, no matter how carefully the ramming is done, and moreover, it requires most close supervision and inspection to be sure that no cement has been squeezed up at the bottom of the joints to cause obstructions in the channel.