Q. I have read several articles recently wherein I see that, like myself, there are a great many plumbers who don't approve of the running-trap placed in the main sewer-pipe, and connected with fresh-air inlet on house side of trap, which seems to be the plan most generally adopted by most of your contributors.

I contend that when the pipe is flushed by a large discharge of water from slop-sink or other fixture, there will be a quantity of foul air discharged from the fresh-air inlet contaminated from contact with foul matter adhering to the inside of pipes, and likely to be carried back into the house through an open window or door. And then what would be the result? Another plumber would be sent for; he would condemn, or the house-owner would insist on its immediate stoppage The trap it is likely they would let remain; then the discharge through the larger traps, not having free passage to sewer or cesspool, would overcome the water in smaller ones, and the air would be discharged into the rooms.

I believe in having the main trapped by all means if possible, but having it ventilated on a different plan, which others might not approve of, but one on which I would like to have practical opinion, and which I will try to explain.

I carry the soil-pipe full size through the roof. Trap all wastes as close to fixture as possible, using all-lead hand-made traps, which I consider best if properly made, excluding running-traps, which I don't think are reliable.

In the cellar, outside of all branches, place a half-s trap, branching the inlet in the back high enough so as to have a perpendicular fall of five or six inches to seal or outlet. Now, instead of carrying the upper part of trap outside through cellar-wall for fresh-air circulation, I return it back with 3-inch pipe through roof, and take a branch from all traps into it as close to the seal as possible, for vent to prevent syphonage and ventilate shorter branches. By not carrying this pipe as high as soil-pipe above roof, and being of different size and in the same atmosphere, they will be of different temperature, which, in my opinion, will insure a circulation at all times, materially aided by every discharge in the soil-pipe. I don't claim that I will have such a draught for my plan as by the former, but I do claim I will have a job that will stand the test of time much better.

This method I have adopted and found it to work well at all times and give entire satisfaction.

A. We have seen great numbers of fresh-air inlets, and have had them in use for years, but we never noticed the slightest odor from the cause suggested by our correspondent. As a matter of fact, a properly flushed and ventilated soil-pipe does not contain a very foul-smelling air. To guard against even such a possibility we have, in our early numbers, advocated that the fresh-air inlet should terminate in a vault with a perforated cover. This contains a sufficient quantity of air to dilute any occasional whiff produced by a reverse current.

The plan proposed of carrying a 3-inch pipe back and up through the roof, and using this pipe also to supply air to the separate traps, would be quite impracticable in our city-built houses. Besides the expense there would be considerable friction to overcome - in some instances quite enough to disturb the seals of the smaller traps down stairs when a water-closet was discharged upstairs. We admit that this 3-inch pipe is better than none at all, but we can assure our correspondent that his apprehension about offense from properly arranged fresh-air inlets are groundless.