SANITATION 397 



and there is a great deal more danger of the pipes clogging 

 between the house and the tank than there is from the outlet 

 of the tank. To save expense and subsequent difficulties, 

 the distance from the wall of the house to the tank should 

 be reduced to a minimum. 



The top of the tank must be somewhat lower than the 

 lowest point in the building from which liquids are to flow, 

 but care must be taken not to get it so low that the effluent 

 cannot flow away from the tank, or that water from the 

 outlet can flow back into the tank at high- water periods. In 

 some instances tanks have been placed very low in order 

 to receive the liquids from the basement, and during rainy 

 periods the water in the outlet ditch became so high that it 

 forced water back through the tank and filled the basement. 

 This is one of the most important factors to be looked after 

 in the location of the tank. Tanks properly constructed, 

 and with a good outlet, will very seldom need any attention 

 or need to be opened. 



Cleaning. It is possible that the tank will need an occa- 

 sional cleaning out. This will depend considerably on the 

 quantity of sand and sediment carried by the water used in 

 the house. Practically all water carries some sediment, 

 which will be deposited in the tank. In addition to this, 

 more or less sand and soil find their way into the tank from 

 washbowls and laundries, owing to the fact that persons 

 working out of doors carry more or less dust in their clothing 

 and on their persons. However, this does not fill up a tank 

 very rapidly. It is exceptional when a tank requires cleaning 

 more than once in five or six years, and many run much 

 longer without any appreciable fill. 



Construction. A septic tank can be constructed of any 

 material that is reasonably water-tight. Where hard brick 

 can be had at a reasonable cost, they can be laid in cement 

 mortar, plastered on the inside, and thus make a very satis- 

 factory tank. Where sand and gravel can be had at 

 a small cost, the concrete tank is the most satisfactory. 



