Connecting Drains. 303 



377. Connecting Sub-main with Main Where a sub-main 

 joins a main the connection should be made at an acute 

 angle as represented at C, Fig. 121, rather than at right 

 angles as at D. If this is not done silt will collect on ac- 

 count of the reduced velocity caused by the meeting of the 

 two streams. It is best in such cases to use the manufac- 

 tured junction tile. 



378. Joining laterals with Main. The junction of a 

 lateral should if possible be made above the axis of the 

 main, .cutting a hole through the main with a tile pick; 

 this is to avoid the clogging of the lateral. Where the fall 

 is great enough to admit of doing so one of the best unions 

 with a main is represented in Fig. 122, the end of the 

 lateral being thoroughly plugged with a stone bedded in 

 clay, or better with 3 or 4 inches of cement. 



i ^ 



FIQ. 122. Method of connecting lator.il with main drain. (After Jul. 



Kuhn.) 



Where, on account of small -fall, the lateral must ap- 

 proach the main low down it should be 'connected in the 

 oblique manner represented in Fig. 121 at C. 



379. Obstructions to Drains. The demand for water by 

 trees is so great that they .must not be permitted to grow 

 within 3 or 4 rods of a line of tile which has water running 

 in it during any considerable portion of the growing season. 

 Fig. 123 represents two bunches of European larch roots 

 taken from 6 inch tile which they had completely closed. 

 A small rootlet entered at the joint, where it grew, branched 



