The automatic siphons used for flushing sewers are characterized in general by the presence, at the base of the discharge branch, of a fixed or movable receiving vessel full of water. This vessel has the inconvenience of breaking the effect of the charge, and the result is that these apparatus do not render the services that might be expected from them. Some of these apparatus have valves, floats, chains, pulleys, and levers. These are still more defective, since their operation is delicate. The parts of which they are composed easily get out of order, and then the reservoir does no more flushing at all. A good automatic flushing reservoir must therefore be of the greatest simplicity, and its parts must be fixed and strong, and the outflow of the water must be rapid and energetic and directly from the reservoir into the sewer. In a word, its construction should be such that there shall be no need of inspecting it, and that its operation be regular. The apparatus devised by Mr. E. Putzeys, Director of Works of the city of Verviers, well fulfills the conditions of an excellent flushing reservoir with an automatic siphon. The siphon has a double curve, but may, however, have different forms according to the various uses for which it may be employed, such as for flushing sewers, urinals, closets, etc. The annexed figure represents the apparatus as arranged for flushing a sewer. The apparatus operates as follows: In the bottom of the branch of the siphon, S, there is always some water, so that, during the filling of the reservoir by means of the cock seen in the figure, the air is compressed in the branch S to a degree that cannot exceed the pressure of an equal height of water to about double the height of the siphon. The reservoir therefore can continue to fill without the water escaping. The submersion of the small siphon, a, b, c, is less than that of the principal siphon, S, and it follows that when the level of the reservoir reaches a height equal to b, a, a new influx, however small it be, causes the discharge of a few drops of water from the auxiliary siphon, a, b, c, which is always full of water. At this moment the water that it contains can no longer resist the thrust of the compressed air in the branch of the siphon, S, and is therefore forced, along with the compressed air, into the flushing pipe. By virtue of the principle of communicating vessels, the water of the reservoir tends to resume its level in the interior of the apparatus, and it then enters with such impetuosity that the siphon, whatever be its dimensions, is primed. The entire reservoir empties instantaneously, and the water flows to open the sewer. From the experiments made at Verviers by the inventor, it results that, with a pipe 10 inches in diameter, the emptying of a 175 cubic foot reservoir can be effected in 30 seconds.