September 30, 2025
If you’re here looking for Gravity Septic System service, you’re in the right place. McNair Septic Design & Consulting is the leading contractor providing gravity septic system design and consulting in Lewis County from our home base in Brush Prairie, Washington. We turn a complex process into a clear plan that fits your site, your timeline, and your budget. Why Choose Gravity A gravity septic system is simple by design: wastewater moves by elevation, not motors. Fewer moving parts mean fewer surprises over the long haul, often lower operating costs, easier upkeep, and a system that just works. When the site allows it, gravity is the most elegant solution. Our job is to confirm whether your property can take advantage of it and to design it so it performs for decades. Fit First: Soil, Slope, and Setbacks Great design starts with the ground under your feet. We begin with site and soil evaluations and, when needed, Perc Testing (Percolation Test) to understand how your soils absorb water through the seasons. We look at elevation drop between your home, tank, and septic drain field, plus required setbacks from wells, water, and property lines. If gravity is viable, we’ll map trench depth, distribution, and reserve area so you meet county standards without overbuilding. If your site has tricky soils or tight space, we’ll show you options, including when an aerobic septic system makes more sense. A Design That’s Tailored, Not Templated No two properties in Lewis County behave the same in winter rains or summer drought. That’s why every gravity septic system we design is property-specific. We size the tank and field for your bedrooms and realistic water use, consider future plans like an ADU or shop, and position components to protect landscaping and access. We’re independent of manufacturers, so you’ll never get steered toward gear you don’t need. The recommendation you get is the one that best fits your land. County Steps, Handled Without the Hassle Approvals can be intimidating if you don’t do them every day. We do. After you approve our proposal, we prepare your application package, coordinate with the county, and line up what inspectors need to see. Our submittals go out quickly, often within two weeks, so your project keeps momentum. You’ll know what’s happening and when, in plain language, with clean drawings you can hand to your installer. What You Can Expect From Us Clear explanations of your options, Gravity Septic System vs. Aerobic Septic System, with pros, cons, and cost implications. Field-proven layouts for your septic drain field, designed for performance and longevity. Transparent timelines and regular updates, so you’re never left guessing. Licensed, insured professionals who’ve designed systems across Southwest Washington for three generations. From First Call to Final Approval We’ll walk the site with you (or review plans for new construction), gather soil data, verify elevations, and design a system that matches how your household actually lives. When decisions pop up, you’re part of them. When questions arise, you get straight answers. And when your permit is approved, you’ll have a design package that’s easy for your installer to bid and build, no head-scratching in the field. Ready for a Gravity-First Plan If you’re planning a gravity septic system, we’ll help you move from “Where do I start?” to “When do we break ground?”, with a design you can trust, county steps coordinated, and a layout that respects your property. We’ll work with you to shape the perfect gravity septic system, from soil science to final drawings, so the rest of the project goes smoothly. Use the quote request form on this page to get started. Tell us about your site and timeline, and we’ll come back with a straightforward scope, schedule, and clear next steps. Start your gravity septic system, request a quote using the form on this page and we’ll follow up with a clear plan and timeline.
