DISPOSAL OF EXCEETA 



373 



closed with a properly prepared cap, Fig. 157, D, and is only 

 used for examining the drain in case of an obstruction. 



Other forms of syphons are seen at Figs. 159-161. In 

 the use of syphons it is a rule that when two succeed each 

 other in the same drain, an air opening must exist between 

 them, as otherwise the action of the second syphon is to 

 suck the water out of the first. 



A Dip Trap was frequently used in old drainage systems. 

 It consisted of a brick chamber containing water, the inlet 

 and outlet being above the water-line ; dividing the two and 



Fig. 158.— Ventilation of stable drains. F, stable trap ; B, stable pipe ; 

 C, disconnecting syphon ; D, sewer pipe ; E, water pipe from roof open- 

 ing over G, grating covering fresh air inlet ; H, access opening. 



dipping down into the water was a tongue of stone. It was 

 a bad form of trap and little better than a cesspool ; further, 

 it was liable to choke and could not be easily cleaned out. 



The D Trap is a metal box like an inverted O, with an 

 inlet which runs under the water contained in the chamber, 

 and an outlet above. It is probably the worst form of trap 

 ever devised ; it is neither self cleansing, nor can it be got 

 at for cleaning purposes — two cardinal points in the matter 

 of traps. 



The Bell Trap (Fig. 162) commonly used in stables is 

 nearly as bad, it is difficult to clean, is readily untrapped 



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