DRAINAGE 



271 



any adjoining roofs and windows, so as to ensure the escape of the foul 

 air and gas into the upper atmosphere. Foul air pipes may be supported 

 by any adjoining building, wall, or tree. The top of the foul air pipe 

 should be protected, against birds nesting in it, by a wire balloon or cap 

 as shown. 



Ventilation pipes should not be much, if any, smaller than the drain 

 pipe which they ventilate. They should never be less than 3£" in 

 diameter internally. They may be jointed to tiie stone ware pipes with 

 bitumen. 



Example of the Disposal of Slop-Water from a Kitchen Sink. — Fig. 207 

 illustrates the arrangements for this purpose. The outlet or waste pipe 

 from the sink is trapped and carried through the wall, that part in, and 



m. 



Fig. 209. 



on the outer side of the wall, being of iron. At the lowest point, 0, of 

 the waste-pipe trap, an orifice should be formed, fitted with a screw plug 

 which can be removed for cleaning purposes in the event of the waste 

 pipe becoming choked. These points are better shown in Fig. 209. The 

 waste pipe discharges openly over a filter bucket, which consists of a 

 square galvanised iron box, without a lid and with a perforated bottom, 

 about 12" square in plan and 12" deep. In this box a layer of dried 

 grass is placed, which roughly filters the slop water before it passes into 

 the drain. The filtering material should, of course, be renewed frequently. 

 The roughly filtered slop- water falls from the filter bucket, through 

 an iron grating and a stoneware hopper, into the grease trap shown, 

 which contains a zinc baler or perforated tray for the interception and 

 removal of any solids that may have passed the filter bucket. As will 



