Septic Tank Design in Lewis County

If you’re here searching for septic tank design service, you’ve landed in the right place. McNair Septic Design & Consulting is the leading contractor providing septic tank design and consulting in Lewis County, based out of Brush Prairie, Washington. We focus on one thing: turning a complicated process into a clear, doable plan that gets your project approved and built the right way.

Start With the Land, Not the Paperwork

A great septic tank design starts with understanding your site. Soil, slope, setbacks from wells and streams, those details decide what will work and what won’t. We begin with site and soil evaluations and can handle perc testing (percolation test) to see how your ground absorbs water. From there, we map options that make sense for your property and your budget, whether you’re building new, adding an ADU, or replacing a tired system that’s reached the end of its life.

The Right System for Your Property

Your property is unique, so the system should be, too. Some sites are perfect for a gravity septic system, simple, reliable, and cost-effective. Others call for an aerobic septic system, especially where space is tight, soils are challenging, or treatment standards are higher. Because we don’t sell equipment, our recommendations are brand-neutral and design-first. You’ll get a tailored layout, from tank sizing to septic drain field placement, that matches your soil conditions, usage, and long-term plans.

Permits Without the Pileup

County approvals can be intimidating. We make them routine. Our team prepares the application, coordinates with the county, and meets inspection requirements so you don’t have to chase signatures or guess what comes next. Once you approve our bid, we move quickly, often getting your submittal filed in about two weeks, so your schedule keeps moving. You’ll see exactly where things stand with timelines and next steps explained in plain English.

Three Generations of Know-How

We’ve been designing systems in Washington since the 1970s, and that history shows up in the details, anticipating challenges before they slow you down and designing for decades of use, not just the first few years. We hold the proper Washington State on-site designer license and carry full insurance, so your septic tank design is handled by people who do this every day and stand behind their work.

One Team, All the Design Pieces

Skip the juggling act. With McNair, you get one partner for the entire design side of your project: site and soil evaluations, perc testing, consulting, full design plans, and coordination through approval. If your property has quirks, steep slopes, clay pockets, seasonal water, limited space, we’ve likely solved them before. Our job is to line up the right solution, not force a one-size-fits-all template.

Straight Talk and Steady Updates

You won’t be left guessing. From day one, we share a simple roadmap: what we’ll do, what we need from you, and when you can expect each milestone. You’ll have room to weigh options, gravity septic system versus aerobic septic system, drain field layout alternatives, build-now vs. phase-later, so the final plan fits your priorities as well as county requirements. Homeowners tell us they appreciate the clarity, and that’s intentional.

Why Homeowners Choose Us

• We turn complex rules into clear action steps.
• Fast, organized submissions keep projects on schedule.
• Designs are tailored to your land and your budget.
• We’re independent from manufacturers, so the design serves you, not a product catalog.
• A long track record of happy clients across Southwest Washington.

Ready for a Straightforward Plan

If you’re planning a septic tank design, let’s make it simple. Tell us about your site, timeline, and goals, and we’ll map a design that fits—complete with soil data, system type, and a clean path to approval. Use the quote request form on this page to get started today. We’ll follow up with a clear plan and timeline, manage the county steps, and keep you informed from first call to final approval. No runaround. No surprises. Just a design that works for your property—and keeps your project moving.

Start your septic tank design—use the form on this page, and we’ll come back with a clear plan and timeline.