"A very short time after the first experimenters had recommended trap-venting other experimenters found several objections to the practice not foreseen by the first in their very hasty recommendations, and the later experimenters similarly published their objections. They found the mouth of the vent pipe, where it connected with the trap, quickly collected sediment, and, especially under kitchen and pantry sinks, very often became completely closed up by grease and fatty vapors. They also found the top of the vent pipe where it passed up through the roof of the house sometimes got closed up by snow and frost, in both of which cases it became worse than useless as affording a false sense of security and standing in the way of the adoption of so-called non-siphoning traps, like the common pot and bottle traps, which at about that time were discovered to be capable of resisting siphoning action entirely and, if built large enough, permanently, without any vent pipe at all.
"More important than all, these later investigators found that the vent pipe, by bringing a constant current of air directly over the water seal of the trap to which it was attached, licked up this seal with a rapidity exactly proportional to its efficiency as a ventilating agent; and so quickly did it in this way destroy the very seal it was delegated to protect that boards of health were obliged soon after the introduction of the trap-vent law to issue circulars to the house owners, warning them of this great danger and directing them to have some reliable plumber refill the traps every two weeks or oftener all through the summer season and at all other times when their houses were closed during the absence of the owners.
"It was also found very soon that the great complication to the plumbing which this custom of trap-venting introduced seriously added to the danger of leakage through bad jointing and the increased use of material, and that it gave rise to dangerous and frequent so-called 'by-passes,' which are blunders in connecting up the vent pipes in such a manner as to open direct communication between the drains and the house.
"These and other grave objections to back-venting led the later experimenters to try very hard to have the trap-vent laws repealed. But it was too late, the people interested did not rush in so zealously as they did before, and Error ran twice round the world while Truth was barely able to cross the threshold.
"At last, however, the defenders of trap-venting, completely driven to the wall, were obliged to admit that the vent pipe did sometimes clog up and did set an air current in motion near the trap seal, and that this current must in time evaporate out the seal, because if the vent were attached to the trap much below the seal it would afford no protection against 'self-siphonage' or loss of seal by 'momentum,' and they were obliged to admit that it added somewhat to the complication and therefore to the danger of bad joints and defective material and arrangement, and they therefore abandoned the advocacy of the law on the ground of protection against siphonage, but still adhered to it on the ground that it was needed to purify the branch waste pipes by aeration.
"But here again they were badly beaten by the opposition. These showed that the branch waste pipes could be infinitely better purified by a powerful water flush followed by an equally powerful pure air flushing from the room through the fixture above the trap than by ventilation with foul air alone from the soil pipe through the back vent pipe. They argued that the plumbing laws should stipulate that every fixture should be constructed on the principle of the 'flush tank' by having outlets and outlet valves large enough to fill their waste pipes and traps full bore at every discharge.
"This was as wise as it was important, but still the matter was not zealously taken up and placed before the legislators, and this simple and useful provision has never yet been incorporated in our plumbing ordinances.
"Nevertheless, there are public-spirited men among the plumbers, as in all callings, and these men have united with the sanitary engineers in condemning the law. One of the ablest plumbers of Boston said to me (confidentially, however, as to his name) that the law was now a gross imposition upon the public, but that the burden had been brought upon them by the early sanitary engineers, and that in all probability it would be left to the sanitary engineers to lift it off again. Many other leading plumbers in different parts of the country have since privately admitted the same thing.
"In 1891 the Boston Society of Architects voted against the trap-vent law and endeavored to have it repealed. But their efforts were without success.
"In section 125 our plumbing statutes stipulate that 'every drain pipe shall be supplied with a suitable trap placed with an accessible clean-out at or near the point where it leaves the building.'
"This involves an inner vent pipe often rising to the top of the house, as shown in our first picture, and sometimes also a sewer vent pipe from the outer side of the house trap, which sometimes again runs to the top of the house.
"Now, cities and towns should invariably be provided with well constructed and well ventilated separate sewerage systems, and the latest discoveries in sanitary science, land irrigation and filtration and in bacteriology have made evident why and how this should be done.
"In well built and fairly well ventilated sewers, like the modern sewers of Paris, the air is perfectly safe to breathe, and these sewers are daily visited by travelers. All sewers should be constructed in this manner, but better ventilated, and the air within them being then entirely innocuous, so far as disease germs are concerned, and in all respects safe in proportion to the extent and liberality of their ventilation, it follows that every house drain should be built of sound, well jointed piping and serve as extra ventilation or breathing tube for the sewers. Hence the use of this main or 'intercepting' house trap should be prohibited by law, cesspools abolished and the sewers improved and perfected with the aid of the money this simplification saves to the public.