When a plan of drains exists, as in the two cases shown on Plates 1, 2, and 3, the difficulty of testing them and proving their defects will not be as great as when no plan has been made. If no plan has been made or no record kept of them, it is best to make a rough plan of the building, fixing the positions of all inlets, their sizes and lengths, of branches to the drains on the premises, and also to lay down on the plan the length and size of this drain to where it reaches the extent of the property or joins the main sewer, opening the ground for testing in a similar manner to that described in Plate 1. In testing pipes or sanitary fittings of any kind, leaks can be easily found by attaching the detector or pressure gauge to the most convenient part of the pipe or fitting, and when everything is sound care should be taken to flush all inlets at the same time, to ascertain whether the rush of water has any effect on the traps or water-seal. If the vibration in the detector or pressure gauge exceeds 2/10ths of an inch, a freer gas space must be provided, or the action of the water checked in some manner. Pipes, whether sanitary or otherwise, can be tested as to tightness in a similar manner. Some modification may be necessary in testing large sewers or the drains of a district, but if the testing is performed in a similar manner to that adopted in the above case the condition of the drains and fittings can be accurately ascertained. The least pressure or suction on the traps of drains or fittings will be shown by the vibration of the liquid in the detector or pressure gauge when the water passes through the pipes with flushing. The term “bad drains” is not exclusively confined to those drains that have leaky joints, or have an insufficient fall, or traps which siphon during the passage of the water, but may also be applied to systems of sewers in general. There are two points in almost every system of drainage that call for some improvement. The first is having the inlets at junctions where small drains join sewers at the side of the sewers. Thousands of traps are being continually siphoned by this cause as soon as the water fills the sewer above the inlet of the branch drain, as this, when filled with water only a short distance, forces gas through the weakest trap, and on the water and soil lowering itself in the sewer, this water acts exactly as the plunger of a pump and draws the water out of the weakest trap. This is often the one in the area or basement of the building, and to avoid this all inlets at junctions should enter the top of the sewers, not for the soil to drop down so as to cause the sewers to silt, but in an oblique direction with the sewage flow. The second point is in the ventilation of sewers, which is not an easy subject to handle. SEWER VENTILATION. The question of ventilation is a very difficult one, whether it is in connection with sewers or buildings.