46. latrines are a series of strong stoneware or cast-iron pans or closet bowls, usually porcelain lined, connected at their bottom by a large pipe which forms part of them and which has a gentle fall to the outlet end. At the lowest end is attached a plunger valve similar to that of the ordinary plunger closet. A trap, which disconnects all the latrines from the drains, is placed under the plunger valve. Water stands in the latrines to a height equal to that of ordinary washout closets, that is, about 5 or 6 inches below the seat. The plunger, which is hollow, acts as an overflow to the latrines.

When the plunger is raised, all the water in the bowls and their adjoining pipes is rapidly drained away, at the same time each bowl is flushed by a separate flush pipe, and when the plunger is replaced the latrines will again fill with water.

Latrines are used chiefly in public places, schools, railroad stations, factories, barracks, hospitals, etc., and they are usually under the control of a janitor.

The bowls should be so formed that excremental matter cannot touch their sides. It should drop in water which will partly deodorize it.

47. Trough closets are essentially composed of a long closet seat with a series of holes in it, having a suitable partition between each, and a cast-iron, brick, or earthenware trough under the seats, which should contain water for the excreta to fall into. The bottom of the trough should be round, and should grade down to the outlet which may have a plunger valve attached, as for the latrines. They are cleaned in a manner similar to latrines. The whole of the internal surface should be flushed by a perforated tube running all around its top, and the solid matter in the bottom should be forced towards the outlet by a large and rapid discharge of water from a jet in the upper end.

When trough closets are flushed from automatic tanks, the plunger valve is omitted, and water to a depth of about 2 inches only is permitted to remain in the bottom of the trough by the aid of an inclined lip near, its point of outlet, similar to the lip which retains water in the ordinary washout water closet.

When such closets are supplied with an abundant and rapid automatic flush, they do good work and require little attention.