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 corrugations in the pipe. Using 4-inch HDPE pipe provides abrasion and corrosion resistance. With lengths of 10 feet, design flexibility is allowed due to the fast installation times. Systems 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. They are available for use in residential and commercial applications. 800/821-6710; www.ads-pipe.com.