If there are no plumbing codes to follow, it is sometimes possible to save money on the plumbing; but unless the specifications are very rigid, there is danger of poor work being installed. By saving money is not meant installing cheap material, but eliminating certain features which most plumbing codes require and which are not essential in producing the best possible type of plumbing system. For example, in most cities the ordinary traps which are required under each fixture to prevent the sewer-gas from returning into the air of the house, after the waste water has drained out, must be equipped with back-vent pipes in order to eliminate dangers of siphonage. The cheap S trap (shaped like an S turned on its side) without this back-venting will siphon out, that is, lose its water-seal by atmospheric pressure pushing the water out of the trap in its attempt to fill a vacuum created by the discharge from a water-closet on the floor above. By back-venting these traps, as shown on page 94, this danger of siphonage is reduced, and, therefore, most codes have adopted this regulation requiring back-venting. But to-day the market offers certain traps which are claimed to be anti-siphonable and which do not require this back-venting, with the consequent result of reducing the cost of the equipment. Most plumbing codes have not changed their old regulations, for many authorities do not yet believe in the possibility of an anti-siphon trap, and so require the use of the back-venting system. Consequently, wherever the small house is constructed within jurisdiction of these laws, the plumbing will cost more than where the anti-siphon trap can be used without the elaborate system of back-venting. Likewise, wherever there is a public sewer, the problem of sewage disposal is simple and cheap; but if the house is not located near any such public convenience, special methods must be employed for the destruction of the waste matter. The best is the septic tank (see illustration) with the small subsurface irrigation tile, through which the partially purified material from the septic tank is distributed under the ground for complete purification by air and bacteria. The other method of disposal—pouring the sewage into a cesspool—is to be deplored, unless there is possibility of an early construction of a public sewer, and no drinking-water is secured from the premises. [Illustration:—SMALL SEWAGE DISPOSAL PLANT—]