recommended where sufficient water can be obtained. In the case of storm or combined sewers advantage should be taken of light rains by damming up the run-off from them in the sewers and flushing with this comparatively clean water. Heavy storms, of course, need no assistance in their flushing effect.

One argument in favor of hand-flushing is that it renders more probable frequent inspection of the system, which will be made at the time of flushing; but on the other hand, pressure of other duties or carelessness may cause longer intervals between flushings than is desirable. In the case of large brick sewers, it is probably best to resort to one of the methods of hand-flushing. For pipe-sewer dead-ends, automatic appliances are desirable in all cases, in the author's opinion. When any flushing is done elsewhere than at dead-ends, hand-flushing is generally resorted to.

ART. 62. CLEANING SEWERS

The purpose of flushing is to prevent deposits, or rather to prevent the accumulation and solidifying of deposits. But if, because of insufficiency or infrequency of flushing, or of the presence of sticks, stones, or other matter which flushing is not adequate to remove, obstructions form, these must be removed by hand or some other method. Catch-basins must be cleaned by hand, and this should be done frequently. The manhole dirt-buckets, also, should be cleaned at intervals. These last are merely removed from the manholes and dumped into a cart. The catch-basins are generally cleaned by ordinary shovels, the dirt being taken to the surface by a bucket and emptied into a cart. Several cities use, for raising the bucket, a block and fall hung on a crane or other support attached to the wagon. In some cities the dirt is mixed with water and pumped out by an Eductor" into a tank-like wagon body, the dirt settling out and the water being used over again repeatedly. In other cities, and especially when the catch-basins are small, the dirt is removed with long- and heavy-handled hoes, the blade of the hoe being at right angles to the handle and about 8 by 10 inches in size. These are used from the surface through the manhole

opening or that left by removing the grating. Catch-basin walls should be thoroughly cleaned with a hose and broom and washed with a solution of chloride of lime or some deodorizer but this is seldom done. The cost of cleaning a catch-basin varies from about $1.50 to $6 each, depending upon their size, the frequency of cleaning, and other special circumstances or conditions, $3 seeming to be about the average for large cities.

Small sewers are cleaned by flushing when this is possible, but in many cases other means must be resorted to. The use of "pills" is convenient where there are no stones, sticks, or other hard materials in the sewer. These are round balls, usually of wood, which are floated through the sewer either in the sewage or, if there is not enough of this, by flushing water. A set of these 2, 3, 4, 5, 7, 9, etc., inches in diameter should be kept or hand. When a sewer is to be cleaned the smallest pill is floated through from one manhole to the next, where it is caught by an assistant; the others are then sent through in the order of their sizes until all have passed through up to the size 1 inch smaller than the sewer. When any ball reaches a point where the opening is contracted by sediment to less than its diameter, the ball, which has floated and rolled along the top of the sewer, dams up the water until it has sufficient head to force its way under the ball and scour out the sediment. The ball rolls slowly ahead, the current washing away the sediment for an inch or two under it. If a stone or stick is among the deposit, the ball may be stopped by it, in which case both stone and ball must be removed by another method. The pill cannot be used when the sewer is stopped entirely so that there is no flow through it. No cord should be fastened to any of these round balls, as it is liable to be rolled about them and wedge them in the sewer, catch in obstructions, and generally give trouble. Ovoid balls, however, are sometimes used with cords attached. These do not roll along the top of the sewer, and may need to be weighted to prevent the friction between them and the sewer top interfering with their motion ahead.

These methods all depend upon the scouring action of the water and presuppose a passage through the sewer. Other

contrivances for cleaning a small sewer under such circumstances are based upon the use of main strength to haul the material out. Probably the simplest is in the shape of a heavy plank disk to which a rope is attached by three short light chains fastened to as many bolts through the disk. One of these chains is attached at each side and one at the bottom of the disk, and their relative lengths are so arranged that when all are taut the top of the disk will incline a little away from the rope. Upon the other side of the disk, at its top, is fastened another rope. By the latter it is pulled a short distance into the sewer, lying flat; the other rope is then pulled, when the disk rises into an upright position and scrapes along the deposit in front of it. It is well not to draw this too far into the sewer at once, but to clean only a few feet at each trip. The dirt can be scraped to a manhole and there removed by buckets. It is awkward pulling in a manhole bottom, and it is well to arrange a pulley in a frame, around which the rope passes, as also around another pulley at the top to permit of a horizontal pull. The lower frame may consist of two 4X6 or 4×8 timbers fastened to each other parallel and a short distance apart, between which the pulley turns in journals fastened to their under sides, these timbers being braced against the inside arch of the sewer and the pulley being in the center of the manhole. This method can be used where the material is too heavy to be scoured out by pills or similar contrivances, and also as a substitute for these.

In some cases the sewer will be found entirely stopped, so that no cord can be got through it, and an opening must be forced through. A rod of some kind is used for this purpose. Since none longer than 5 feet can be got into the sewer through the manhole (unless it be too flexible for efficient service) rods of this length made to join together are generally used. These are sometimes lengths of gas-pipe with screw-couplings, but wooden rods 3 to 5 feet long, with a peculiar hook or other patent coupling are furnished by several firms. These are forced through the obstruction by working them back and forth or even by driving with a hammer. When an opening is once made, it is well to leave the rod in it and work it a little back and forth as the

sewage flows through until the hole is too large to be in danger of immediately stopping again, when a pill or cord may be floated through and the cleaning completed by one of the above methods.

A small sewer or sub-drain may also be cleaned by the use of hose, pushed into the sewer while kept stiff by the water flowing through it.

FIG. 63.-SEWER CLEANING TOOLS USED IN RICHMOND BOROUGH, NEW YORK. Sewer cleaning brushes, root cutters, clay cutters, claw, and other applicanes. can be fastened to jointed rods shown in bag.

These

In some cases the obstruction may be so obstinate as to necessitate the digging up of the sewer. Before doing this, its exact location should be ascertained by pushing a rod to it through the sewer and measuring its length, or by the use of mirrors, as previously described.

For cleaning house-connections, sub-drains, and other small. pipe which cannot be reached readily, garden hose is excellent, sufficient water being turned through it to make it stiff enough

to be pushed through the pipe; or rods may be used, as just described. Instead of a rod, the city of Waltham, Mass., has used for these cases a length of steam-hose filled with sand, a wooden plug being fastened in the end of it. This is flexible, but stiff enough for use in a pipe only 3 to 5 inches in diameter.

Even pipe sewers as small as 18 inches diameter can be entered for inspection and cleaning by hand. A large stone or a stick wedged across the sewer can frequently be removed in this way and the necessity for digging up the pipe avoided.

If the sewer is found to be broken in any place, there is generally but one thing to do-to dig down to and replace it. A sewer which is only cracked or is leaking badly has been repaired by inserting inside of it a line of screw-joint pipe as large as can be slipped into it, and sealing the space between the two at the ends with cement. The substitution of new pipe would probably be cheaper in most cases, however.

When small pipe is only coated or contains but little deposit, it is sometimes cleaned by the use of a wire brush, just the size of the sewer, fixed upon the end of a rod similar to those already described. Small sticks, jute, etc., can be cut by tree-pruning shears. Cloth or similar matter can be withdrawn by a contrivance like a large corkscrew on the end of the rod. These and other special contrivances are shown in Fig. 63.

The cleaning of sewers large enough to permit a man to work in them needs no special discussion. If they are large enough, the dirt may be carried to the manhole in a low car running on the sewer bottom. In smaller sewers it may be shovelled or hoed into a pile at each of two manholes from a point midway between them, and removed in buckets.

An inverted siphon may be cleaned as an ordinary sewer, after the sewage flow has been diverted to the other siphon-pipe or dammed up, and the sewage contained in it pumped out.