or more water-closet flushes, or that of two large bath-tubs when emptying themselves in two minutes. This connection may be of vitrified clay pipe from the sewer to a point 5 or 6 feet outside of the cellar wall. It should be laid to as perfect line and grade as was the sewer itself, the fall of 1: 40 being the minimum allowed under any but exceptional circumstances. If a uniform grade from the sewer to inside the cellar is not obtainable or desirable, or if this distance be more than 100 feet, it is advisable to place an inspection-hole at the fence-line or at some other convenient point, the grade and line being straight each way from this to both sewer and house. If the pipe branches before reaching the house, an inspection-hole should be placed at the junction. The joints of the house-connection should be of cement, and it should be of equally as good material as, and laid in every way according to the methods used for the sewer. In made ground or quicksand or where trees are near the pipe or the latter passes near a well or cistern, the connection should be of cast-iron pipe with lead joints.

ART. 60. MAINTENANCE REQUIREMENTS

The requirements for keeping a sewerage system in good running order can be concisely stated as-preventing and removing deposits and maintaining ample and safe ventilation.

As previously stated the main dependence for preventing deposits is flushing. If a deposit remains for any time, it is apt to continually increase and become more difficult of removal, and deposits should therefore be removed as soon as possible after forming. This the automatic flush-tank is supposed to do for 800 to 1000 feet below it, but any forming below this limit will probably need to be removed by hand-flushing from a manhole or by the use of special appliances. If deposits continually form in any one place and are not apparently occasioned by articles which should not be introduced into the sewer it may be advisable to place a flush-tank just above where such deposits form, at one side of the sewer but connected with it at a manhole or by a Y branch. If obstructions are frequently formed at any

one place by the introduction of improper matters, such as' ashes, bones, etc., the source of these should be ascertained and the parties responsible therefor punished.

It should not be taken for granted that a sewer is working properly, but the system should be inspected once a week or at least once a month. This may require merely a look into each flush-tank to see that it works properly, into each inlet or catchbasin to see that it is clean and the grating unobstructed, and into each manhole (the dirt-pan being at the same time removed and emptied) to see that the sewage is flowing with sufficient velocity and is apparently not dammed back by any deposit below. But during the first few months of his service the inspector should enter each manhole and look through the sewer at each inspection until he becomes familiar with its condition of depth and velocity of flow when in good order If there are any considerable odors observed about any appurtenance the cause should be discovered and removed. This will usually be a large deposit or imperfect ventilation, except in the case of catchbasins, where it probably means improper or infrequent cleaning.

The catch-basins should be cleaned after every rainfall. There is danger of putrefaction and objectionable odor from these if this is not done within two or three days after each rain, but this is almost impracticable in large cities, where there are one or two on every corner, without the use of an enormous number of men and carts, since each cart with three men will clean but five to fifteen catch-basins a day

A record should be kept of all sewer-inspections, each line of sewer and each appurtenance having a record of its own showing when it was inspected, its condition, when cleaned, what repairs were made to it, with their nature and cost; of the frequency of flushing or of the discharge of each automatic flush-tank; of the location and date of making each houseconnection, with all details as to route, size, and grade of connection-pipe, cost, by whom ordered, by whom put in (if by private contractor).

Extensions of the system should, of course, be made with as much care as were the original sewers, and no alterations

should be made in the original plans without a careful consideration of their effect upon the sytem as a whole.

ART. 61. FLUSHING

When automatic flush-tanks are used, they should be inspected at intervals to insure their regular discharging. The most common failing with siphon-tanks is the trickling over of the water into the sewer as fast as it enters the tank after it has once reached the level of the top of the bend. Under this condition the siphon will never flush. This trickling may be due to faulty designing, but is usually caused by a leaking joint or blow-hole in the iron siphon at some point, which must be corrected. The frequency of discharge is regulated by the cock admitting the water. This can be adjusted only by actual trial with each tank. It is a good plan to have one or more registering reservoir-gauges for occasional use in the flush-tanks which will indicate the times of discharge. A simple one, but sufficient for this purpose, can be made with a clock-works actuating a vertical cylinder on which the height of water is constantly registered by a pen whose motion is caused by the rise and fall of a float, a cord carrying the pen and one from the float both passing over connected wheels of such relative diameters that the path of the pen is but 4 or 5 inches long. Such an apparatus left for a day or two in a flush-tank will serve in place of frequent visits to it, and can be moved from one to another as each is adjusted to the desired frequency of discharge. The waste of water caused by flushing oftener than once in eighteen to twenty-four hours is not justified by any proportionate advantages.

In flushing directly from 2- or 4-inch branches led from the water-main into the flush-tank, the valve is ordinarily opened to its full extent, or so much as is necessary to maintain the height of water in the flush-tank as great as is safe for the tank or sewer. It may be left open until such time as the water flowing through the manholes below is perfectly clear. It will be necessary to use the most solid construction in the flush-tank to resist the

considerable force with which the water leaves the waterpipe.

Instead of connecting the flush-tank with the water-main by a large pipe, a small one is sometimes used, and the tank filled from this after closing the sewer end, which is then opened and the contained water allowed to flush the sewer. This method takes much longer than the previous one and is consequently more expensive. In some cases the flush-tank is filled by hose from the nearest fire-hydrant.

In some cities the water is conveyed to the flush-tanks in carts, and either the tanks filled from these and discharged by hand as above, or from the bottom of the cart a large pipe or canvas hose is lowered into the flush-tank and connected with the end of the sewer, into which the water is discharged under a head equal to the elevation of the cart above the sewer. These carts are ordinarily used at manholes along the line of the sewer rather than at flush-tanks proper.

As flushing is seldom effective for more than 800 to 1000 feet below the point of entrance of the flushing-water, when automatic tanks are not used at the head of every section of such length which requires flushing, this is performed at manholes wherever necessary. For this purpose, outside water may be introduced by carts as just described; or all the openings in a manhole may be stopped and the manhole filled by hose, when the plug to the down-stream opening is removed and the sewer below flushed; or only this opening is closed, and the sewage is permitted to back up in the sewer above, when the plug is removed and the sewage performs the flushing. The last method is not particularly satisfactory with pipe sewers in most instances, since there is thus obtainable only a small head and resulting low velocity of flush, and if the house-connection pipes are on a flat grade the sewage may back up these to an undesirable height. Deposits also may form while the sewage is accumulating, which will not be removed by the flush if near the upper end of the dammed sewage, and the time required for a sufficient volume of sewage to collect will often be considerable and is longest in those cases where the necessity for flushing is greatest.

The plugs used for stopping pipe and other small sewers may have any of a variety of forms. One design is a simple conical cork-shaped piece of wood with heavy rubber so fastened around it as to come between it and the inside of the sewer when the plug is pushed into place and make a watertight joint. Another consists of a solid center of plank, around the edge of which is placed a pneumatic tube similar to a bicycle tire, which is inserted just inside the sewer and the tire inflated by a bicycle pump. These have ropes attached by which to draw them out of the sewer when the manhole or flush-tank is full, the air being first released from the tube of the one last described.

Another plan, that of bracing a loose frame or hinged gate against the end of the sewer in a manhole, is hardly applicable to properly constructed systems, where the manhole-channel and sewer are continuous, but may be used in a flush-tank designed for the purpose. The cover, whether loose or hinged, may be held in place by a brace hinged at the middle and extending from the cover across the flush-tank to the opposite wall. A rope is attached to the hinge of the brace and by pulling this when the tank is full the brace folds up and releases the cover.

In large sewers it is generally impracticable and unnecessary to dam back the sewage higher than, or even as high as, the crown of the sewer, and a dam one-half or two-thirds the height of the sewer is sufficient. This may be made similar to those already described, but not filling the entire bore of the sewer. Or a "pocket dam" may be used. This consists of a bag of tarred canvas having rings around its mouth and a rope passing through these long enough to reach from the sewer to the surface. Another rope is fastened to the bottom of the bag. This bag is filled with water and placed in the sewer-invert, being held upright by the rope through the rings, and serves as a dam to the sewage. When the sewage has risen sufficiently, this rope is released, the bag collapses and is removed by the rope attached to its bottom.

In very large sewers, flushing, if practised at all, must generally be done with sewage, on account of the enormous quantity of water required for this purpose. But this practice is not