Q. What is the best size of soil-pipe for an ordinary city house, and should not traps be larger than the pipe to allow water to flow through them easily? I have been told they should be.

A. Four inches is large enough for such pipes. The traps should be no larger, for they would then become cesspools to a certain extent which is to be avoided. In fact, a 3-inch trap would be more cleanly than a 4-inch one, and preferable on this account for most water-closets, provided a good air-vent be provided.