CONSTRUCTION 



145 



To prevent the washing or tramping of earth about the 

 outlet, and to give strength, a wall of masonry or concrete 

 should be built something as shown in Fig. 55. 



FIG. 58. Two devices for protecting drain outlets. A, trap of galvan- 

 ized iron hung by common door hinges. The serious objection to 

 the trap is that it interferes with the entrance of air to the tile sys- 

 tem. B, screen of j-inch iron rods, hung, in this case, by chain 

 links. Devices of this nature are especially desirable when surface 

 water is let into the tile system. 



191. Screen. Means should be provided to prevent 

 vermin, such as rats, from entering the mouth of the drain. 

 To accomplish this, a screen of woven wire, or a grate of 

 iron bars mounted on or in a strong wooden frame, should 

 be firmly set against the outlet. (See Fig. 57.) It will 



