AFig. 30.B.
A.—Section showing a Good Method of connecting Soil-pipe to Drain by Brass Thimble.
B.—Outer View, showing Brass Thimble wiped on to Soil Pipe.
The upper end of the ventilating pipe should be made to open remote from any window. It may have a cowl attached to it, but it is doubtful if this materially aids the aspiration of foul gases. It is wise to cap the upper end of the ventilating shaft with a dome of large meshed wire-netting to prevent birds building their nests in it.
The connection of the soil-pipe with the closet-pan is its weakest point, and the most liable to leak. The main difficulty consists in forming joints between earthenware and metal. Socketed connections are not safe. The use of an india-rubber ring inserted between the lead and earthenware flanges and bolted together by means of a brass collar and hooked bolts makes a fairly good connection. Various screwed connections are made. In another form the earthenware collar is covered outside with lead, so that a soldered joint can be made between the earthenware trap and the soil-pipe. In the “metallo-keramic joint” the earthenware joint is painted over with a metallic solution and fired. To the metal film thus formed, lead or other metal can be firmly soldered.
The connection of the soil-pipe into the socket of the first pipe of the earthenware drain requires also to be carefully made. This pipe is curved, and at its upper end has a socket, into which the soil-pipe enters. A length of brass or copper tubing known as a “thimble” (about a foot long) should be soldered to the bottom of the soil-pipe; the rim of this thimble rests in the socket of the drain-pipe and the space between the two is filled with Portland cement (Fig. 30A). With the ordinary connection between lead soil-pipe and drain, the former is apt to become dented by blows, and the latter is very liable to be partially blocked by the dropping of cement inside the pipe when making the joint.
The House Drain under ordinary circumstances receives waste water from sinks and baths, rain-water, and the discharge from the closets.
Fig. 31.
Showing Depth of Fluid and consequent Flushing Force of Three Drains containing an Equal Quantity of Sewage.
We may consider drains under the following heads: material, form, joints, gradient, ventilation, trapping. The first essential is that they should be water-tight, so that their contents do not percolate into the surrounding soil. Socketed glazed stoneware pipes and iron pipes best fulfil this condition. The best material for making stoneware pipes is Devon or Dorset, or similar fine clay, which makes a very strong pipe. Tested pipes free from cracks and flaws must alone be used. The pipes should be laid in straight lines, each pipe being arranged with the spigot and not the socket end directed towards the flow of sewage. The fall should not be less than 1 foot in from 40 to 60. If the fall is less than this amount, artificial flushing from the upper end of the drain is necessary. Usually branch drains are made 4 inches in diameter, the main house-drain having a diameter of 6 inches. A larger size than this is seldom necessary. Thus if A, B, and C be three drains with an equal fall and conveying an equal amount of sewage, the rate of travel and therefore the flushing force will be greater, because the depth of the fluid is greater, in A than in B, and in B than in C. Small drains are more completely self-cleansing than large drains. The water-tightness depends on the character of the joints. In this respect iron drains present the great advantage over earthenware that there are fewer joints and that these can be rendered permanently water-tight without difficulty by being run with blue lead and well caulked. To render an earthenware drain water-tight, (a) it must be laid on a solid bed of cement concrete at least 6 inches thick, so as to prevent sinking, and under the house it should be covered with an equal thickness of cement concrete (I, Fig. 29). (b) The joints must be made with extreme care, the best Portland cement being used for the purpose. Clay is inadmissible, as the fibrils of tree-roots easily find their way through it. The inside of the joint must be raked by the workmen, before the next pipe is laid, to make sure that no fragments of hard cement are left projecting in its interior. Such projections are not uncommon causes of subsequent blockage. Various patent joints have been used, but they are no better than the above when properly laid. Just before the drain leaves the curtilage of the house and near its junction with the sewer, it is trapped, and on the house-side of the trap (E, Fig. 29) an inlet ventilator is provided. The general arrangement should be studied in Fig. 29.
Ventilation of the house drain from end to end is important, a free escape of foul gases out-of-doors being induced. The exit is provided by carrying the soil-pipe up full bore above the eaves, and remote from windows. One opening alone would not induce a current of air, and the other end of the drain being trapped from the sewer (B, Fig. 29) it is necessary to provide an inlet for fresh air at E. This may be placed a few feet above the ground or at the ground-level. Usually a mica-flap valve is provided at its upper end, which closes whenever a puff of foul air attempts to escape from the drain. The necessity for this is doubtful. Ordinarily air enters at the inlet and circulates through the drain, escaping at the upper end of the soil-pipe ventilator.