8 
BULLETIN 1408, U. S. DEPARTMENT OF AGRICULTURE 
be made as for a lamp hole or like the top of the surface water 
inlet shown in Figure 3, C. Elimination of the expensive reducer 
may be accomplished by use of a concrete ring placed in the bell and 
having its inside diameter the same as the interior of the small pipe 
used above. (See pi. 1, A.) For large lines, manholes had best 
be used. 
LATERAL CONNECTIONS 
Main lateral connections should be made with manholes, but for 
small connections angle boxes will serve the purpose. On a system 
having a great many closely-spaced farm laterals, it probably will 
be necessary to eliminate these structures and simply make a hole 
in the upper part of the main lateral to receive the end of the small 
farm lateral. This joint should be well surrounded with pieces of 
4x4 
Cross 5/7 Is 2*6 
A 
B 
-Piles to suit 
conditions 
4*4' 
wH-tyJ 
■3-0' 
DIMENSION 
TABLE 
Size of Pipe 
4*4' 'Stringers rough 
D 
A 
B 
10" 
.8" 
18" 
12" 
9" 
20" 
IS" 
ir 
22" 
18" 
13" 
24" 
20" 
14%" 
26" 
24" 
i&y 2 " 
28" 
-Alternate Joints- 
f 
-2"x6 l 
3'-0"- 
Fig. 5. — Cradle for supporting large tile in soft ground 
broken tile and gravel or concrete. The elevation of the top of 
the small lateral should be near that of the top of the line to which 
it is connected. If possible, branch lines should be provided where 
numerous small farm laterals are needed, as it is not advisable to 
connect these with main trunk drains. 
OUTLETS 
Structures are usually necessary at outlets of unclerdrains to prevent 
injury from frost and to afford protection of adjacent banks. For 
drains with diameter of 16 inches or less a continuous section of 
wood box or corrugated pipe will be satisfactory (pi. 1, D). This 
should be from 14 to 20 feet long, depending upon the slope of the 
bank and nature of the material. A tight box made of 2 or 3-inch 
lumber will prove economical. However, boxes are likely to be 
