MISCELLANEOUS FARM CONVENIENCES 239 



which leaves the sewer open to the atmosphere and pre- 

 vents the possibility of back-pressure that might drive 

 the poisonous gases from the decomposing sewerage 

 through the sewer back into the house. In this way, the 

 septic tank is made entirely separate from the house 

 plumbing, except that the two systems are connected at 

 this outside trap. 



It is sometimes recommended that the waste water 

 from the second compartment shall be distributed 

 through a series of drains made with three-inch or 

 four-inch drain tile and that the outlet of this set of 

 drains shall empty into or connect with a regularly 

 organized field drainage system. Generally speaking, 

 the final discharge of liquid from a septic tank that is 

 properly constructed is inoffensive and harmless. How- 

 ever, it is better to use every possible precaution to pre- 

 serve the health of the family, and it is better to dis- 

 pose of the final waste in such a way as to prevent any 

 farm animal from drinking it. 



While manholes are built into septic tanks for the 

 purpose of examination, in practice they are seldom 

 required. If the tanks are properly built and rightly 

 proportioned to the sewerage requirements they will 

 take care of the waste water from the house year after 

 year without attention. Should any accidents occur, 

 they are more likely to be caused by a leakage in the 

 vitrified sewer than from any other cause. Manufac- 

 turers of plumbing supplies furnish the siphons to- 

 gether with instructions for placing them properly in 

 the concrete walls. Some firms supply advertising 

 matter from which to work out the actual size and pro- 

 portions of the different compartments and all connec- 

 tions. The making of a septic tank is simple when the 

 principle is once understood* 



