Having treated upon the subject of drainage generally, we now come to the consideration of house-drainage, which requires a few remarks. The old system of carrying the house-drainage into the main-lines, consisted simply in lay ing down a drain from each house, connected at the one end with the sinks, water-closets, &c. ; and at the other with the main sewer, which ran in the centre of the road. Amongst the recent improvements, a new plan has been adopted, by which the drainage of the house is conducted into a pipe at the back of the premises, and by it into a main sewer ; this is termed back-drainage ; and the old system,front-drainage ; for whereas in the former case, the sewage is collected at the tn the tatter it is collected at the front of the houses. The system of back-drainage is certainly in many respects an improvement upon the old, but it is not so universally applicable as some persons would lead us to believe ; it pro vides a convenient variation, but not an extensive substitute. One great improvement is effected by carrying the drainage at once away from the premises, instead of its running under them, as before. The objections to the old system in this respect, are, the passage of the drains under the houses, whereby, if not perfectly constructed, the effluvia is likely to be spread all over the interior ; and the inconvenience which is thereby occasioned in case of stoppage, or other necessary examination or repair which involves the removal of floors, &c., and the opening of drains in the house; matters not only inconvenient, but sometimes dangerous, on account of the escape of effluvia. In some cases, where the old brick drains have been employed, and, as is not unfrequently the case, improperly constructed, the drainage has been allowed to escape through crevices in the brick-work, and saturate the foundations of the premises ; this is fFequently the cause of damp basements, and of unpleasant and noxious odours in the lower part of the house. A further objection exists in the frequent apertures required to be made into the main sewer for the insertion of the house-drains, and the many interruptions which are occasioned in the flow of the sewage in the main sewer, by the discharge of so great a number of house-drains.
These objections are obviated almost entirely by the new system ; the drains, instead of being carried through the house, are at once removed from it, and the dangers and in convenience attending the old practice entirely done away with. Such at least is the case in by far the majority of instances: occasionally, where the position of water-closets in front of the house requires the drains to be brought through the house to the back, the employment of the new system would not be so advantageous; the carrying of drains from sinks through the house, is not so objectionable. The large sewers will not be interfered with, except at distant intervals, for the insertion of the main back-drain, discharging the sew age of a block of several houses. There are several other
advantages attending the new system, amongst which may be mentioned the following:—The flow of sewage is very con siderably improved by its concentration into one drain, in stead of being spread over many; the frictional surface is also much reduced. In the old system, the occasional flow of water from each house was so inconsiderable as to produce a mere dribble, which flowed sluggishly, and deposited its solid matters in abundance, under the very dwellings; it was but a small portion that eventually reached, and was discharged into the sewer; whereas, where the back-drainage is adopted, the water is discharged almost immediately into the main back-drain, and the collection of the sewage of all the houses therein produces a considerable volume, sufficient at all times to keep up a moderate flow into the main sewer, and thus prevent deposit ; if, however, deposit should occur, it is less objectionable than where it takes place under the house. There is a fair objection to this system when stoppage does occur, for the stoppage in one place will occasion the same in every house which happens to be situate between the stoppage and the first inlet ; under the old system, this would not take place. In the separate system, each occupier is sub ject to the inconvenience occasioned only by his own negli gence or carelessness, whereas in the combined system he is, to a certain extent, at the mercy of his neighbours; when, however, we take into consideration the improved flow in the main back-drain, and the less probability of stoppage, this objection will not have so great weight.
It will also he frequently found, that a considerable length of drain is saved by adopting the combined system, and where this is the ease, back-drainage is decidedly preferable; for not only is the expense lessened, but the fall is likewise improved, and the contents are more rapidly and more effi ciently discharged. Where length of drain can be effected by back-drainage, there can be no question as to its adoption; yet there are some instances in which this is not the case, but the contrary rather; and under such circumstances, con siderable discretion will be required in selecting that system which shall be most efficacious..
The drains employed in carrying the sewage from the houses, need not be more than four inches in diameter, of the same material and descriptions as those above recommended for sewers ; 6 or 9-inch pipes will generally be found of suf ficient capacity for the main back-drains, but of course this will depend upon the number of houses drained into them. These should be trapped at their entrance into the sewers, to prevent the effluvia rising through them from the sewer into the houses.• Sinks, water-closets, &c., should also be trapped at the inlets.
We are now arrived at the close of this article; and we are sure that the increasing importance of the subject will excuse the length to which it has been carried.