WATER SUPPLY, PLUMBING, ETC., FOR COUNTRY HOMES. 35 
If the sewage is applied continuously and in such quantities that the 
system is kept saturated, the filter or disposal area becomes water- 
logged and "sewage sick" and ceases to be effective. It is therefore 
necessary that the final treatment system be of sufficient capacity to 
dispose of each dose of sewage quickly. 
DOUBLE-CHAMBER SEPTIC-TANK SYSTEMS. 
The septic tank for a small sewage-disposal system should ordi- 
narily consist of two chambers. In this type of tank the sewage is 
received, settled, and partially purified in one chamber and collected 
and discharged from a second chamber. This type of tank if properly 
designed should give satisfactory operation, since the sewage in the 
settling chamber suffers little disturbance, and the discharge to the 
final disposal system may be made intermittent by means of an auto- 
matic siphon placed in the discharge chamber. 
Practice indicates that the settling chamber of a small septic tank 
should have a capacity' of from 5 to 15 cubic feet or from 40 to 80 
gallons per person in the family. Some allow an average of 10 or 11 
cubic feet per person. The best results are obtained when the 
capacity approaches the larger limit, so that 18 to 36 hours' sewage 
from the house may be held at one time, thus causing the sewage to 
remain in the tank and undergo sedimentation and bacterial action 
for this length of time. But care should be taken not to make the 
tank so large that liquefied sewage will remain in it more than 36 
hours, for in that event putrefaction is likely to set in. For this 
reason one should make an accurate estimate of the daily sewage 
flow, which will be practically equal to the daily water consumption. 
Although a depth of 3 feet may be sufficient for some classes of sewage, 
it is better to have the depth from 4 to 8 feet, according to the 
number of people, in order to give the sludge a good chance to settle 
and liquefy. The width of the chamber may ordinarily be about 
one-third or one-half the length, although this may vary for economy 
and convenience. The width should not be less than 3 feet, however. 
The inlet from the house should be provided with an elbow, so that 
the discharge will be at least a foot below the contained sewage, thus 
preventing disturbance of the surface scum. The outlet from the 
settling chamber should be equipped in the same way. Where the 
entrance and discharge velocities are very strong, baffle walls of 
wood or concrete should be placed before these openings to break the 
current. These precautions are especially beneficial in the smaller- 
sized tanks. 
