Lee's Liquid Waste Services - Trenches Free Advice Keep water from roof downpipes and paved areas away from the absorption field. If the field is flooded, the soil won’t be able to cleanse the wastewater from the septic system. Have a plumber fit an effluent filter to the septic tank outlet to keep solids in the tank and extend the life of your trenches. Only plant grass near the absorption / transpiration / aspiration / distribution field – roots from larger plants such as trees and shrubs are likely to damage the trench – and mow it regularly. Don’t drive or park on any part of the absorption area. This will compact soil and may crush the pipes and trench domes. Grow nutrient-tolerant plants near drain fields and irrigation areas. Build a small earth bund wall (a small ridge) about 15 cm high that is longer than, and uphill from the trench area to divert surface runoff water around it.