272 FARM BUILDINGS IN SOUTH AFRICA 



be clear, from the water-seal shown shaded in the drawing, the grease 

 trap acts also as an intercepting trap which shuts off foul sewer gases and 

 prevents their entering the house. 



CE is a cleaning eye to give access to the drain for cleaning purposes. 

 Since it is on the down-stream side of the water seal, it must be airtight. 

 The stoneware lid is therefore sealed by a thin layer of 1 : 1 cement 

 mortar on top of it, which can easily be broken when the eye requires to 

 be opened to give access to the drain. 



It will be noticed that the grease trap, hopper, etc., are bedded in 

 concrete, and that a concrete curb is formed, round the mouth of the 

 hopper, on which the filter bucket sits. 



A 6 -inch diameter grease trap 24 inches deep, such as that shown, 

 with grating, hopper, and perforated tray complete, costs about 32s. 

 in Johannesburg. Grease traps can also be had 9 inches, and 12 inches 

 in diameter. Like the other stoneware goods mentioned in this chapter 

 they are manufactured in South Africa. 



Immediately down-stream of the grease trap, a foul air outlet pipe, 

 takes off, which may be attached to one of the walls of the building 

 and should rise a few feet above the eaves of the roof and above all 

 windows. 



The 4-inch drain pipe should have a fall of not less than 1 in 40. 

 If it discharges freely in air, say into some water-course, no special fresh- 

 air inlet will be required, since the open end of the pipe itself will serve 

 for this purpose. If, however, it discharges into a French drain, a mica 

 flap fresh-air inlet should be provided near the end of the drain pipe, 

 close to the French drain, as shown. 



A French drain, sometimes called a Vivian Poore drain, is a device 

 much used in South Africa for effectively getting rid of slop water. In 

 its simplest form it consists of a trench dug in the ground and filled, 

 to a level just above the end of the drain pipe entering it, with rough 

 stones of about the size indicated in the drawing (Fig. 207). These 

 stones are covered with a few sheets of corrugated galvanised iron, 

 arranged so as to prevent sand or earth from falling into the trench. 

 The corrugated iron sheets are covered with a layer of earth to the 

 original ground level. It should be evident that a French drain will 

 be more efficient in light sandy or loamy soils, than in clayey ground. 

 The size of French drain required depends mainly on the nature of the 

 soil, and on the amount of slop-water to be disposed of. An ordinary 



