Q. Will you please advise me what means plumbers in your city take to prevent condensation filling vent-pipes and making them no good? It is not always possible to give them a steady pitch.

A. They are so arranged that there are no pockets or traps in them, and so that the water of condensation can flow back to the waste-pipe in some way. It sometimes requires considerable ingenuity to accomplish this, but that should be exercised every day in the plumbing business.