A temporary chokage in a small-sized sewer which does not arise from any structural defect can be speedily and effectually remedied by the use of Ben Reed’s patent drain-cleaning rods, which are probably too well known to every town surveyor to need any description, but in conjuction with man- or lamp-holes and straight lines of sewers they are very valuable.
Before closing this chapter, a few words upon what is called the “separate system of sewerage” may be of use.
The mistake hitherto made has been to try to absolutely separate all rainfall from the sewers, and there is no doubt that a partial separation of the rain-water from the sewage proper has many advantages; but it must be understood that a great deal of the rain-water that falls upon roofs of buildings and in back yards and small back streets must of necessity be carried into the sewers, as well as liquid refuse from manufactories. A partial separation thus carried out has the following advantages:
(1.) It is not necessary to have sewers of enormous diameter.
(2.) The depth of the surface water conduits need not be so great as that which is necessary for sewers.
(3.) The avoidance of road detritus being washed into the sewers.
(4.) Where the sewage has to be pumped or treated chemically or put on the land, the combined system causes an immense unwieldy bulk of liquid to be at times dealt with.[186]
(5.) The sewers may be placed at the back of the houses, a great advantage which cannot be carried out under the combined system.
(6.) The regularity in the amount of flow of sewage.
(7.) The accuracy with which the quantity of sewage may be calculated and the sizes of sewers apportioned.