The system your site will take
A septic system is not really a purchase decision. Which type you can put in is decided by the ground, and the single measurement that decides most of it is how much suitable native soil sits beneath where the drain field would go. Soil is what actually treats wastewater; the less of it you have, the more the system itself has to do the work instead, and the more equipment that takes.
That is why the table below reads as a ladder. Every row down is less soil to work with and more machinery to compensate. A designer and the health department determine which rung your site is on, from a soil and site evaluation, and the answer is not something a homeowner or a contractor gets to pick. Depths and descriptions here are the Washington State Department of Health's own. Types of systems · EPA, types of septic systems
| System | Native soil needed | How it works |
|---|---|---|
| Gravity system | 3 ft or more | The simplest design and the most common one in this region. Waste separates in the tank, heavy solids settling into sludge at the bottom and lighter material rising into a scum layer at the top, and the liquid in between flows out to the drain field under gravity alone. No pump, no power, nothing to fail electrically. The soil does all of the treatment, which is why it needs the deepest profile of anything on this list. |
| Pressure distribution | 2 to 3 ft | A pump chamber sits after the tank and pushes the liquid out in measured doses, spreading it evenly along the drain field lines instead of letting it run to the nearest low point. Even distribution means thinner soil can still do the job. The trade is a pump and a high-water alarm: better treatment, and a moving part to maintain. |
| Sand filter system | 1.5 ft | The liquid is pumped into a sand-filled box, where it trickles down through gravel and then through sand before going out to the drain field. The sand does the treatment the ground would otherwise do. |
| Mound system | 1 to 2 ft | A drain field built up above the natural ground level inside a constructed sand mound, dosed by a pump for even distribution. It is the answer to shallow soil, a high water table or shallow bedrock, and it needs the space to build the mound. |
| Aerobic treatment unit | 1 to 1.5 ft | A blower injects air into the tank, which greatly increases the aerobic bacteria doing the treatment, so the liquid leaving the unit is cleaner than a conventional tank's. That is what makes it usable on thin soil, on small lots, and close to surface water. Washington requires these to be inspected at least annually, sometimes more often, by a manufacturer-certified representative. |
| BioFilter | 1 ft | A proprietary treatment system that stands alone and needs no separate drain field component. Design, installation and maintenance all have to be done by professionals approved for that product. |
Two things follow from the ladder, and they matter more than which name applies to you. The first is that a more complicated system is not a worse one; it is the system that a thinner soil profile requires, and it is doing more treatment than a gravity system does. The second is that the machinery comes with obligations, and those obligations are the part most people are not told about before the work starts. That is what the next section is about. Very large designs, over 3,500 gallons a day, are regulated separately by the state as large on-site sewage systems. LOSS program
What each type costs to own
This is the part of an installation decision that nobody quantifies, and it is the part we can evidence. Every inspection on both counties' systems is filed as a public record, so the service history of about 39,000 gravity systems, 11,000 pressure systems and 9,000 complex ones is on file. What it shows is that the difference between system types is almost entirely a difference in upkeep, not in risk. Every figure below is measured from those filings.
| Measure | Gravity | Pressure | Complex or proprietary |
|---|---|---|---|
| Median gap between pump-outs observed | 3.09 years | 2.95 years | 1.72 years |
| Inspections that found a problem | 21.9% | 19.1% | 19.5% |
| Inspections on record, 2015 to 2025 | about 49,000 | about 20,000 | about 38,000 |
| Properties in the two counties | about 39,000 | about 11,000 | about 9,000 |
Put over the twenty years someone might actually own the house, the gap stops being a percentage and becomes a schedule. On the pump-outs alone, which is what these records measure directly, a gravity system is looking at roughly six visits and a complex one about twelve. Inspections widen it further, though not by a single number: the state rule already asks for an inspection every three years on a gravity system and every year on anything more complex, King County evaluates anything non-gravity every year, and Pierce County adds a risk classification that sets how often the result is reported — annually at high risk, every three years at moderate. An advanced system lands in the frequent end of both, which is worth knowing before it goes in rather than after.
Do advanced systems fail more?
No, and the figures are closer than almost anyone expects. Across every inspection filed in the two counties between 2015 and 2025, a complex or proprietary system was recorded as deficient on 19.5% of inspections. A pressure system, 19.1%. A plain gravity system, 21.9%. Three percentage points separate the most and least complicated designs in the region, and the simplest one is at the top of that range rather than the bottom.
We would caution against reading that as gravity systems being worse. Gravity is the oldest stock in the region by a wide margin, and an older system has had longer to develop a problem. We hold no installation date for the overwhelming majority of these properties, so we cannot separate the age of the system from the design of it, and we are not going to claim we can. What the numbers do support is the narrower point: choosing between system types, where a site even allows a choice, is a decision about how much maintenance you are taking on, not about how likely the thing is to fail.
New systems start clean
There is one more thing the records show clearly, and it is reassuring if you are about to spend heavily. When a newly built system is inspected and signed off, it almost always passes.
| Measure | Figure | What it covers |
|---|---|---|
| Commissioning inspections that found a problem | 4.2% | About 500 new-system sign-offs on record |
| Routine and point-of-sale inspections that found a problem | 17% to 19% | Established systems, for comparison |
A caveat on how to read that, because the two figures are not measuring the same population. The 4.2% is a new system being checked at the moment it is commissioned, before anything has had time to go wrong, and about 500 sign-offs is a small base next to the hundreds of thousands of filings behind the rest of this page. It says a new install in this region is very rarely handed over faulty. It does not say anything about how that system behaves in year fifteen.
Where advanced systems are actually needed
System type is recorded for most properties in King County but only a minority in Pierce, so a local mix can only be published where the records support it. The 29 towns below are the ones where enough properties have a type on file to say anything honest; the shares are of properties where the type is recorded, not of every property.
The column worth reading is the last one. Gravity dominates everywhere, from about half to nearly nine in ten of typed systems, so "most systems here are gravity" is true in every town and tells you nothing. The complex share is what varies, and it is a fair proxy for how often local ground forces an advanced design, and therefore how likely you are to inherit the annual inspection cycle rather than the three-year one.
| Town | County | Septic homes | Type on file | Gravity | Pressure | Complex |
|---|---|---|---|---|---|---|
| Redmond | King | 3,761 | 73.2% | 49% | 22% | 29% |
| Woodinville | King | 6,385 | 67.8% | 58% | 18% | 24% |
| Carnation | King | 1,268 | 74.8% | 51% | 26% | 23% |
| Duvall | King | 1,045 | 69.5% | 54% | 24% | 22% |
| Black Diamond | King | 720 | 64.4% | 48% | 31% | 21% |
| Vashon | King | 3,367 | 62.4% | 58% | 21% | 21% |
| Fall City | King | 1,076 | 77.7% | 60% | 19% | 21% |
| Maple Valley | King | 2,641 | 70.7% | 63% | 18% | 19% |
| Longbranch | Pierce | 581 | 61.6% | 54% | 27% | 19% |
| Snoqualmie | King | 429 | 76.7% | 70% | 14% | 16% |
| Renton | King | 4,616 | 71.1% | 73% | 11% | 16% |
| Sammamish | King | 2,426 | 74.4% | 69% | 17% | 14% |
| Enumclaw | King | 2,584 | 62.8% | 71% | 16% | 14% |
| Fox Island | Pierce | 1,473 | 54.2% | 65% | 21% | 14% |
| Kent | King | 4,121 | 65.8% | 72% | 15% | 13% |
| North Bend | King | 2,354 | 79.2% | 70% | 17% | 13% |
| Auburn | King | 5,841 | 64.9% | 73% | 13% | 13% |
| Issaquah | King | 2,418 | 75.9% | 70% | 17% | 13% |
| Ravensdale | King | 868 | 67.5% | 52% | 36% | 12% |
| Gig Harbor | Pierce | 16,738 | 54.6% | 63% | 24% | 12% |
| Seattle | King | 1,103 | 69.8% | 76% | 13% | 12% |
| Bellevue | King | 1,076 | 70.9% | 74% | 14% | 12% |
| Kirkland | King | 911 | 60.7% | 79% | 11% | 10% |
| Covington | King | 1,185 | 66.3% | 83% | 8% | 9% |
| Vaughn | Pierce | 569 | 55.4% | 66% | 25% | 9% |
| Lakebay | Pierce | 2,377 | 53.3% | 72% | 20% | 7% |
| Federal Way | King | 2,865 | 62.6% | 82% | 11% | 6% |
| Des Moines | King | 609 | 66.3% | 88% | 8% | 4% |
| Burien | King | 1,524 | 63.1% | 87% | 9% | 4% |
The advanced-system cluster at the top of that table is not scattered. Redmond, Woodinville, Carnation, Duvall, Fall City and Snoqualmie sit next to each other across the Snoqualmie Valley and east King County, which is a real feature of the ground out there rather than a coincidence in a spreadsheet. If your property is in that band, an advanced system and an annual inspection are a realistic expectation rather than an unlucky outcome.
When replacing beats repairing again
Most people arrive at a new system through a failure rather than a new build, which makes the honest question not "can this be fixed" but "how many times am I going to fix it". The records have something useful to say there, and it does not require a single price.
Repeat problems are common and they concentrate. 11.8% of septic properties in the two counties have two or more deficiencies on record. Close to 190 properties have ten or more. And 22.2% of all deficiencies recorded between 2015 and 2024 have no repair filed against them at all, which is partly a paperwork gap and partly problems that were never dealt with.
There is one more piece of context. The share of inspections that fail at the point of sale, which Washington requires whatever the system type, rose from 17.9% in 2018 to 24.9% in 2024. We want to be careful about what that does and does not mean: it shows failures at sale becoming more common, and it does not show that a failed sale inspection causes a replacement. Treat it as the backdrop to the decision, not as an argument in it. The one thing we would say plainly is that a third or fourth repair on the same component is worth a conversation about replacement, and an inspection is what tells you which conversation you are in.
What is changing in the rules
Anyone installing now is doing it in the middle of the biggest set of changes to Washington's on-site sewage rules in years. The state rewrote its rule in 2024 and the provisions are still phasing in, King County adopted a revised code in 2025, and Pierce has issued new guidance on top of a code that itself dates from 2018. What follows is what each authority has actually adopted, with a link to its own page so you can check it rather than take our word for it.
- Washington State
- The State Board of Health adopted a rewrite of the on-site sewage rule, chapter 246-272A WAC, on 10 January 2024, filed on 1 March 2024. It is coming in by stages rather than all at once: most provisions took effect 1 April 2025, approval of maintenance service providers came in on 1 February 2025, and the new property transfer inspection requirement does not take effect until 1 February 2027. The revision also covers local management plans, field verification of proprietary products, remediation, repairs and minimum lot sizes. If you are planning a sale in the next few years, the 2027 date is the one to note. Rule revision
- King County
- The Board of Health adopted a revised Title 13 in February 2025 and it has been in effect since 1 April 2025. It changes the design of new and replacement systems, the maintenance of existing ones, and oversight of the trade. Two specifics the county calls out: all septic tank lids must now be secured, and a technical memo corrects the design flow used for houses with more than three bedrooms, which can change the size of system a larger house needs. Revised OSS codes
- Pierce County
- New systems are governed by the Health Department's Environmental Health Code Chapter 2, On-site Sewage, adopted July 2018, alongside the state rule. It is the document that sets the soil and site evaluation (Section 18), what an application has to contain (Sections 27 to 29), and the installation, inspection and approval-for-use steps a new system has to pass before anyone can use it (Section 30). Ongoing inspections come from two rules at once. The state rule sets the inspection the owner must have done — at least every three years for a septic tank with a gravity drain field, every year for anything more complex — while Chapter 2 (Sections 38, 39 and 42) assigns each system a risk classification that sets how often the result is reported to the Health Department: annually at high risk, every three years at moderate risk, and at low risk only before a Report of System Status, after a new system is installed, or on notification by the health officer. Qualifying owner-occupied gravity systems can apply to move a three-year cycle to five, provided the property is not on a shoreline. Newer than the code itself: operation and maintenance guidance effective November 2024, and revised tank replacement requirements from October 2025. Environmental Health Code Chapter 2 · Applications and forms · Reduced inspection frequency
None of this is something you have to navigate yourself. A new system is designed by a licensed designer, permitted by the county, and signed off by the county before it can be used, and the people doing that work are the ones who track which provisions are in force on the day your application goes in.
Septic installation and replacement
These are the septic services we offer across Pierce and King County. Installation and replacement sit at one end of a range that starts with finding out what your system is actually doing.
- Septic System Installation
- Septic Tank Installation
- Septic Drain Field Installation
- Septic Replacement
- Septic System Repair
- Septic Inspections
- Septic Pumping
- Septic System Cleaning
- Emergency Septic Services
- Plumbing
How an installation or replacement starts
It starts with knowing what you have and what the ground will take. For a replacement that means an inspection and a diagnostic by one of our certified technicians, so the conversation is about a system that actually needs replacing rather than one that needs a repair. For a new build it means a soil and site evaluation, which is what determines which of the system types above your property can take.
We do not publish a price for installation, and we would rather say why than leave a blank. An install is priced off the design, and the design comes out of the soil evaluation, the size of the house, the lot and which county you are in. Anyone quoting a figure before that work is done is guessing. Once there is a design, there is a real number, and we will walk you through it in plain terms alongside what each option involves.
Inspections are recommended for routine maintenance, troubleshooting issues, or preparing for property transactions. Early detection can help avoid more costly repairs later.
Why Choose Upfront Septic & Plumbing
Upfront Septic & Plumbing is built on reliability, transparency, and quality service. We show up when we say we will, explain the work clearly, and provide honest pricing. Our goal is to deliver long term solutions, not quick fixes.
We take pride in serving local communities and building lasting relationships with our customers through dependable service and professional results.
If you need septic pumping, plumbing services, or 24 hour emergency septic service, Upfront Septic & Plumbing is ready to help. Contact us today to schedule service, request an inspection, or get immediate assistance.
Methodology
About this analysis. Washington requires every on-site septic system to be inspected on a fixed cycle, and the inspection must be carried out by a county-certified operation-and-maintenance specialist who files a report with the health department. Those filings are public records, which is what makes the service-burden figures on this page possible.
This analysis covers more than 518,000 filings for over 144,000 septic properties in Pierce and King counties, as recorded by the Tacoma-Pierce County Health Department and King County Public Health. System type is derived from those accumulated service reports, so it is known for most King County properties and a minority of Pierce ones. That is why the local mix is published for 29 towns and not for all 45.
Definitions and limits. A deficiency is an inspection filed with a status of Deficient; severity is not recorded, so a deficiency may be anything from a missing riser lid to a failed drain field, and it does not mean a system has stopped working. A failure rate is deficiencies as a share of inspections filed, not of properties. The records begin when a system is first serviced, which means they hold no installation cost, no permit data, no soil or design data, and no installation date for most properties. Nothing on this page about system types, the installation process or the rules comes from our records; all of it is cited to the Washington State Department of Health, the US Environmental Protection Agency, King County Public Health or the Tacoma-Pierce County Health Department. Figures are as of 22 August 2026. Individual property owners are not identified.
