A standard drain consists of a system of several perforated plastic pipes connected in parallel. Their purpose is to distribute the treated wastewater evenly to the filter layer, which should just be made of gravel or small crushed stone. An alternative to such a solution are infiltration boxes, which do not require a gravel layer. The number of boxes depends on the number of people using the system and the permeability of the soil. More information and selection instructions can be found in the guide.