We have considered briefly the various agencies which tend to destroy the seals of traps, and have presented several vital objections to the methods of protection generally attempted.
Internally all kinds of mechanical seals, balls, gates and valves, both single and double, as shown in
Figs. 64 to 81, inclusive, have been tried. Externally ingenious and complicated devices for refilling the seals after their destruction, like that shown in Figs. 135 and 136, have been attempted. But all of these devices have failed for want of simplicity and reliability.
Finally the "back vent" pipe was conceived of, and for a time it was supposed that the great remedy had been attained. A few rough and unscientific laboratory tests made on siphonage, which seemed to corroborate the idea, at once gave rise, in several large cities, to a law rendering special trap venting obligatory. At the time this law was enacted the common "round" or "pot" trap of large size had shown itself to be capable of resisting siphonage when new and clean, but it was recognized that under some conditions, as when used with kitchen and pantry sinks, clogging was certain in time to render it inoperative. The object of the vent pipe was to afford protection without the use of these cesspool traps, but the practical result has been that cesspools have become, since the enactment of the law, more prevalent than ever, because not only has the use of the pot trap, under various changes of form and name, continued undiminished, but the mouth of the vent pipe has added a cesspool to traps which were otherwise substantially self-cleaning, as has already been shown.
Thus not only has the original purpose of the law been frustrated, but the very evil it was intended to remove has been actually augmented by it. The pot trap is converted by grease into an S trap, and the S trap by the same agency acting in the mouth of the vent pipe, into a cesspool trap. The vent pipe was applied to protect the S trap, but is itself destroyed by the very same agency which destroyed the pot, and the only wonder is that this inevitable result was not anticipated before the law was passed.
Having now found this belief in back venting to be fallacious, safety must be sought in some other direction.
Siphonage must be guarded against, not by adding to the trap a limb of indefinite length and connecting it with the external air, but by forming the trap itself in such a manner that its own water-way shall serve as a special air-vent passage, and permit the air of the room to supply the partial vacuum in the soil pipe without drawing the water out of the trap before it.
If a trap can be devised which shall be as self scouring as a straight pipe of the size of the waste pipe itself, and at the same time be capable, unvented, of resisting a siphoning strain powerful enough to completely empty an S or small pot trap fully vented in accordance with the law, and if the construction of this trap is such that it forms its own vent pipe and causes fresh air to pass through its own body whenever it is used and whenever siphoning action occurs, so that it actively assists the main soil pipe vent in aerating the waste pipe system in the most effective manner; then it becomes clear that the continuance of this law on the statute books is a very gross imposition upon the public. When, in addition to this, we know that the vent pipe is utterly unreliable on account of clogging and other influences already fully described, and that it involves the very positive and important objection of rapidly destroying by evaporation the seal it was intended to protect; where other simpler methods now known are entirely free from these difficulties; the enforcement of such a law becomes an inexcusable outrage upon the public, whether such enforcement be due to selfish private interest or unjustifiable ignorance, and the investigation of the whole matter by an impartial commission appointed by the Federal, State, or Municipal authority, becomes a very serious duty in behalf of the people which has already been far too long neglected.
Although it has always been declared impossible, from the nature of things, to render a simple unvented S trap absolutely secure against siphonage this has nevertheless now, in effect, been fully accomplished.