Water closets should always be flushed with water from a flush tank, or through a specially constructed flush valve of large area that is supplied with water through a distributing system separate from the one that supplies the other fixtures in the building. There are three reasons for these requirements: First, the flush pipe or flush valve will be of sufficient size to supply a large volume of water in a short period of time, thus insuring a good flush; second, the tank can be proportioned or the flush valve regulated to furnish a certain quantity of water at each flush; and third, when connected in this manner and the water is shut off from the building, opening a faucet at a lower level cannot siphon foul air or water from the closet bowls into the supply pipes and afterward discharge it at other fixtures.

Fig. 148

Flush tanks are made with capacities ranging from 6 to 12 gallons. In large city apartment houses, hotels and like buildings, where a considerable volume of water is generally flowing through the house drain, tanks of smaller capacity may be used than would be required in private houses or in large country institutions that are located a considerable distance from a trunk sewer or other place of sewage disposal. The reason for this is that in large city buildings if a sufficient volume of water is provided in closet tank or flush valve to discharge the contents of a closet into the soil stack, it will fall by gravity to the house drain, where assisted by the flowing water in the drain, it will be carried to the street sewer. On the other hand, assistance from other sources cannot be depended upon in private buildings and country institutions, so a sufficient volume of water must be provided that will carry the contents of the closet bowl all the way to the street sewer. Closet tanks with siphon flush valves are generally used in connection with washdown, washout and hopper closets, while slow-closing flush valves are used with siphon jet combinations. To insure sufficient force to thoroughly scour and flush a closet bowl, flush tanks must be set at least seven feet from the floor to the bottom of tank.

Fig. 149