will join. There should be no slope to the bottom of the manifold trench. Sand filter trenches should be dug only when the ground is dry and there is no possibility of smearing of the trench bottoms. The trench bottoms should slope away from the manifold at a grade of no more than one-eighth inch per foot. If dosing is to be used, the trench bottoms should be level. Install the septic tank and dosing chamber. CONVENTIONAL SYSTEM MODIFICATIONS Place the bedding sand if it will be needed. Place the side liner if one is to be used; otherwise, place the filter sand in the filter trenches. If no side liner will be used and there is the possibility of effluent bypassing the filter sand and running out the sides of the trench above the sand surface, hollow out a basin in the sand to direct the effluent downward (Figure 6.23). Cover the sand with 2 in. of coarse gravel. Check the slope of the gravel surface at this point. Its surface should be at the level of the bottom of the distribu- tion manifold trench, and should be level if dosing will be used. Now, flood the filter sand with water. This is quite necessary to prevent future settling of the sand and rearrangement of the distri- bution system. Do not, however, tamp the sand to settle it, since this might affect the bottom surface permeability. Next, place the various pipes in their respective trenches. Connect the manifold supply pipe from the septic tank or dosing chamber to the manifold, and backfill and compact the manifold supply pipe trench. Then connect the other end of the pipe to the dosing cham- ber or septic tank. Finally, connect the distribution pipes (holes down) to the mani- fold, and cover the distribution pipes with the final 6 in. of coarse gravel. Add a layer of untreated building paper, filter fabric, or 6 in. of hay or straw on top of the gravel, and backfill the filter trenches and the manifold trench. If the backfill is rocky, protect the manifold pipe with sand before backfilling that trench. At this point, it is wise to flood the filter trenc