Available in configurations of nine, 11 and 13 pipes, Septic Stack units from Advanced Drainage Systems allow for soil contact without the use of gravel. This pipe is engineered with holes and slots, allowing it to collect and disperse the effluent as it passes over the corrugations in the pipe. Using 4-inch HDPE pipe provides abrasion and corrosion resistance. Its 10-foot lengths and design flexibility help decrease installation time. They are lightweight and have a high storage volume with structural strengths that will support an H-10 load rating with 12 inches of settled cover. Applications include trench low-pressure piping, pressure distribution, and trench, mound, and bed configuration. 800/821-6710; www.ads-pipe.com.