rs can be selected once the total dosing rate is known. Using Table 6.6, the minimum diameter of the laterals can be deter- mined. For example, using 4-ft spacing of three-sixteenths-inch ONSITE WASTEWATER DISPOSAL Table 6.6 Recommended Lateral Distribution Pipe Diameters (in.) Lateral Length Hole Diameter (in.) 3-Ft Hole Spacing 1 1/4 1 1/4 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 4-Ft Hole Spacing 1 1/4 1 1/4 1 1/4 1 1/4 1 1/4 1 1/2 1 1/4 1 1/2 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/2 1 1/4 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/4 5-Ft Hole Spacing 1 1/4 1 1/4 1 1/4 1 1/4 1 1/4 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/4 1 1/2 1 1/4 1 1/4 1 1/4 1 1/2 Data Source: U.S. EPA. holes on laterals 25 ft long would allow 1-in. diameter PVC to be used. The manifold should be larger than the laterals, and rather than bother with the gyrations involved with finding the smallest diameter pipe that might work, 2-in. PVC should be used. Usually, CONVENTIONAL SYSTEM MODIFICATIONS the manifold won't be over 12 ft long anyway. Two-inch pipe should be used for the supply pipe as well. Going to 1.5-in. pipe would add more than 2.5 ft of head to the pump requirement to overcome the additional friction loss in 100 ft of pipe. Another source of friction is the resistance to flow from fittings and bends in the pipe. If your distribution system has more curves than a snake in a cornfield, add 10% or SO to the friction losses from the supply pipe, manifold, and laterals rather than calculating the exact additional losses. Otherwise, the frictional losses due to the fittings can be ignored. Pump selection is an important step. A pump which is too small for the job will have a short lifetime; a pump too large is a waste of money. In our example, we are looking for a pump that will deliver 27 gal per min at the distribution laterals. To do this, the pump must (1) lift the effluent from the dosing chamber to the trenches