Q. Will you please inform me what you consider the proper diameter (interior) for a water-closet trap? I find many of the closets of recent make contract the diameter of the trap to three inches, or even less. While a pipe of this diameter has the advantage of more thorough scouring at every flushing, and might prevent many things from entering the soil-pipe which have no business there, would it not be liable to be clogged when large or stiff paper is used, especially in public places? On the other hand, if the diameter of the trap is too large, the body of water to be moved is heavier, the scouring less, and, where 3-inch soilpipes are used, as is now occasionally seen, danger of obstruction therein is greater. For hopper-closets should you consider 3 1/2-inch a good dimension?

A. As 4-inch seems to be the size of soil-pipe most used, it is desirable that the outlet of a hopper or water-closet should not exceed 3 1/2 inches. With good flushing, we do not apprehend any trouble from stoppage, even if the outlet is only three inches.