Sewer pipe delivers sewage from a house or building to a public mainline sewer pipe, a septic system or a leech field. Laying a gravelless line is no different than laying a standard line other than the fact that gravel is not used to bed the pipe. Laying pipe is a three-part process: determine the rate of fall and dig the trench, lay the pipe and bed it, and backfill. Without gravel, you must bed the pipe with sand.
Determine the rate of fall from the starting point of your sewer line to the ending point. A stubbed sewer line coming out of a building that requires connection to a septic tank -- for example -- must fall at a rate between 1/8- and 1/4-inch per foot. Measure the difference in elevation between the starting and ending point with your laser level. Measure the horizontal distance from the two points. Divide the elevation difference by the horizontal distance. If the rate of fall does not meet or exceed that range, make modifications before the starting or after the ending point of the line you lay. If it falls within that range, dig your trench.
Dig a flat trench that drops at a constant rate, equal to the sum of your division between elevation and distance. This ensures your trench drops your pipe at the proper rate of fall from start to end. Use your laser level to measure the rate. Compact the bottom of the trench with the heel of the hoe's bucket as you move to prevent soft dirt from compacting after you back fill and put a sag in your line.
Lay your pipe. Start at the low end of your trench. Primer the coupler, tee or elbow at the septic tank and one end of one stick of sewer pipe. Put glue over the primer on each and slide them together. Hold them together firmly for at least 10 seconds. The chemical reaction between the glue and primer pushes the two joints apart if you do not. Move uphill, glue a coupler to the other end of your first stick and glue another stick to the coupler. Continue uphill until you reach the starting point.
Bed the sewer pipe with sand. Pour it over the top and sides with at least 3 inches of cover. The bedding gives the pipe protection and a little flexibility to move as you back fill. Backfill the trench with the material you removed during excavation. Once the trench is full, wheel compact it with the backhoe by driving back and forth over it.