The receiver of the ejector should be vented, such vent usually being connected into some convenient main vent on the gravity-drainage system. Air compressors and a storage tank for compressed air are necessary features of a plant of this kind.

The valves on the inlet and outlet pipes of the ejector are for use in the event that it is desired to disconnect any one of several sewage lifts that are connected together on the same system. The automatic sewage lift is generally installed in a brick or iron well and made accessible in case of inspection and repairs. In handling the low-level sewage of some of the immense hotels of the large cities, apparatus must be used which is able to discharge many thousands of gallons of sewage each hour.

This may be accomplished by means of ejectors of the type shown in Plate 46, by connecting several of the lifts together.

When so connected, combination lifts working under either compressed air or steam are generally used, in order that in the event of a breakdown on one source of motive power, the other may at once be made use of. It will readily be seen that no chances can be taken in providing against a mishap which may totally disable an entire system of this kind, for it is a question of handling a great many thousands of gallons each hour, and when this cannot be done, and the sewage constantly accumulates at this high rate, the situation becomes very serious.

When several ejectors are connected together, the main sewage inlet divides the sewage between the different ejectors, and each one discharges into a main.

Some of the advantages of this method of disposal are the following: No pumping apparatus, with working parts to get out of repair, is necessary; there are practically no working parts in the lift to get out of order; the receiving tank, in which the work of the apparatus is chiefly performed, has no finished surfaces or parts on which the coarser matter in the sewage may act injuriously; and the tank acts as a trap to protect the building against the entrance of gases from the sewer.

In addition to the matter of caring for fixture drainage, subsoil drainage, floor drainage, etc., must also be provided for. This drainage is usually disposed of by other apparatus than that used in connection with polluted drainage, the apparatus being known as the automatic sump tank, an illustration of which appears in Plate 46. This tank is installed in a water-tight catch basin or pit, constructed of brick or iron. Subsoil, floor drainage, and any other clear-water drainage that must be taken care of, should enter the pit through inlets provided with check valves, as shown, all drains being trapped in the usual manner. The tank should be air-tight and vented, generally into some convenient main vent in the gravity system. The action of the automatic sump tank is similar to that of the automatic sewage lift already described.

When the bucket is raised by the drainage in the tank to the right height, it opens the compressed-air supply valve and closes the vent pipe, the admission of compressed air forcing the contents out of the tank and into the main gravity line.

A wise provision in the installation of automatic sewage lifts on large work, is that they shall be provided in pairs, each being large enough to hold the drainage accumulating from the fixtures during an hour. The two ejectors should be so connected that they will operate alternately. When water closets discharge into sewage ejectors, the vent from the apparatus should not be less than 4 in. in diameter, and when other fixtures only are connected into it, the vent should be of the same size as the main waste pipe serving such fixtures.

There is another form of ejector sometimes used, which discharges low-level sewage into the house sewer of the regular system, also by means of compressed air.

The compression of the air in this apparatus, however, is accomplished by the head of the sewage in the gravity system discharged into a large tank. Water from the public water supply may also operate this system, and this water afterward be used in supplying fixtures on the floors below the sewer level. This system, while not particularly well known, has the advantage of disposing of the sewage without apparatus which entails expense in installing and in operating.

Of the several different methods mentioned or described for raising low-level sewage, the automatic sewage lift, operating by compressed air, with steam as an auxiliary, is, in general, the most desirable.

In order to determine the size of lift needed for any given plant, the amount of waste entering it must be known, and to estimate this it is necessary to know the number and character of all plumbing fixtures below the sewer level, the number of floor drains, and the character and size of all other drains and apparatus from which waste of any description is discharged.

It is also necessary to know the size of the gravity house sewer, and the kind of power that is to operate the lift, with full data concerning pressure, etc., relating to such motive power.

In addition to its use in connection with underground floors of high buildings and underground public toilet rooms, there are several other uses to which the automatic sewage lift may be put.

It often happens that small villages or hamlets, situated in level country, which has no advantages for disposing of public sewage by gravity, are in a perplexing situation. The sewage lift may be used to advantage under such conditions.

By installing it in a pit underground, as low as desired, enough pitch can be obtained to allow the discharge of the public sewer into it. The lift may discharge the sewage into a septic tank at a higher level, and this tank in turn onto filter beds, the latter delivering the clear sewage which results, into underground distributing pipes. More concerning the septic tank, filter beds, and underground distribution will be found under following plates.

If other sources of motive power are not available, the lift may be operated by water.

The sewage lift is used in many marine plumbing systems also. The apparatus is located below all fixtures, which discharge into it by gravity, the lift discharging the sewage into the sea.

This is an important application, as the disposal of sewage of large steamships, as well as other vessels, is a matter of importance and difficulty.