The Septic Stack System from Advanced Drainage Systems is available in configurations of 9, 11 and 13 pipes. The units allow for high soil contact without using gravel. They function as a trickle filter, dispersing effluent into the voids in and around the specially banded pipe. This pipe is engineered with holes and slots, allowing it to collect and disperse the effluent as it passes over corrugations in the pipe. Systems are available for use in both residential and commercial applications in trench, bed and mound configurations, as well as pressure dosing. 800/821-6710; www.ads-pipe.com.