The exhaust, draw-off, drip, and blow-off from a steam boiler should never connect directly into any sewer or into any part of the drainage system. These pipes should discharge into a tank or condenser, the capacity of which should be the same as that of the boiler. The tank should be provided with a vent pipe not less than 2 in. in diameter, connecting with the outside air. The tank should connect, through a waste not less than 3 in. in diameter, into the house drain or sewer, preferably the latter. The waste should be trapped and vented and provided with a back-pressure valve. The reason that this class of drainage should not discharge directly into the drainage system or sewer is that the steam rising from it produces sewer pressure, against which all possible precautions should be taken. Water over 120 degrees in temperature should not be discharged into the sewer, owing to the result which may follow in the formation of steam.
The drainage from hot-water heating systems and from low-pressure steam-heating systems may, however, be connected directly into the drainage system, if properly trapped, without entering a condensing tank.
The drainage from hydraulic elevators, lifts, and other similar apparatus which is direct connected, should not be discharged directly into the drainage system, but should first enter a tank, in order that it may be discharged from that point into the sewer without pressure. Tanks used for this purpose should be trapped and vented and provided with a back-pressure valve.