Septic records in King County, Washington

We hold 184,607 septic records for King County, Washington. Of the parcels we have classified here, 84,437 are on septic and 486,662 are on sewer.

Where King County, Washington septic records are kept

King County, Washington publishes onsite-wastewater records through a county-built portal. Records can be searched without an account.

County records portal

What a septic record contains

A permit file usually holds the as-built drawing: tank location and capacity, drainfield layout and size, the soil evaluation, the system type, and the approval date. Almost every septic job starts by finding that drawing.

Pumping and maintenance

A pumper needs the lid location and tank capacity. Without the as-built, locating a buried lid is guesswork billed by the hour. Pumping interval is driven by tank size and household size, both on the drawing. A tank pumped too rarely pushes solids into the drainfield, and a ruined drainfield is the expensive failure, not the tank.

Designing a septic system

A design starts from four inputs, and three of them are usually already sitting in the county record for a developed lot:

• Design flow. Almost every state code sets daily flow from bedroom count, not square footage or occupancy. Flow is what drives everything downstream.
• Soil and site evaluation. Percolation rate or soil profile, depth to seasonal water table, depth to restrictive layer, and slope. This determines the application rate, and so the drainfield area. On a lot with an existing permit the original evaluation is often in the file, which can save repeating the work.
• Tank capacity. Sized from design flow, with minimums set by code. Two compartments are standard, and an effluent filter is required in many jurisdictions.
• Dispersal method and setbacks. Conventional trench, chamber, bed, mound, drip or an engineered alternative where soils are tight or the water table is high, plus the required distances to wells, property lines, surface water, foundations and any replacement area.

Repair and replacement designs work the same way but start from the recorded as-built, because the existing tank, field footprint and any reserve area constrain what can be built.

Commercial and multi-family systems are the same logic scaled: design flow comes from a fixture or use-type table rather than bedrooms, tanks get larger with traffic-rated lids, grease interception is added for food service, and a licensed engineer typically stamps the drawing.

Installation and permits

Installation normally requires a permit issued before work starts, an inspection while the system is still open, and a final as-built submitted on completion. That final drawing is the document that ends up in the county file, which is why records exist at all.

Inspection, sale and transfer

Most lenders, and many counties at point of sale, require an inspection. Inspectors start from the recorded as-built: without it they are probing blind, and time-of-transfer inspections are commonly where a failing system is discovered. Buyers should pull the file before closing, not after.

Repair and replacement

A repair designer needs the original system type, the soil evaluation and the existing layout. Where the original drainfield area is known, a replacement area is often already reserved on the drawing.

Drainfield protection

Pools, sheds, driveways, fences and heavy vehicles over a drainfield destroy it. Root intrusion does the same slowly. The setbacks and the field footprint are on the drawing, which is the cheapest possible way to avoid the most expensive failure.

Cost

Costs vary by soil, system type and local code, so we do not publish a price for this county. What the record does tell you is the system type and drainfield size, which is what any contractor needs before quoting rather than guessing.

Septic companies in King County, Washington

426 septic and onsite wastewater businesses we have on record in King County, Washington: pumping, installation, design, inspection and repair. Listing is not an endorsement and we take no fee from any of them.

Getting septic work done here

Whatever the job, the recorded file is the cheapest first step:

• Pumping. The pumper needs the lid location and tank capacity. Finding a buried lid without the drawing is billed by the hour.
• New installation. Requires a soil evaluation, a design sized from bedroom count, a permit before work starts, an inspection while the system is open, and a final as-built.
• Repair or replacement. Starts from the existing as-built, because the current tank, field and reserve area constrain the design.
• Inspection for a sale. Inspectors work from the recorded drawing; without it they probe blind.
• Soil and site evaluation. Percolation or soil profile, water table depth and restrictive layers determine the drainfield size.
• Riser, filter and alarm work. Cheap preventative jobs that need the tank detail off the drawing.

Designing or replacing a system here

Designing a system here is free to try. We build a code-referenced septic design from the parcel itself: design flow from bedroom count, tank sizing, soil-driven drainfield area, dispersal method and setbacks, rendered as a drawing you can take to a county reviewer. Where a recorded as-built exists we start from it rather than from assumptions. Generating and viewing a design costs nothing.

Open the design tool

More for King County, Washington

• Septic companies in King County, Washington — pumping, installation, design, inspection and repair
• Septic rules in Washington — who regulates it, the permit sequence, who may design and install
• Buying or selling with septic in Washington — inspections and transfer requirements
• What septic work costs — what drives a quote before you accept one
• How often to pump a septic tank
• How to find your tank and drainfield
• Commercial and specialty systems
• This county as JSON — machine-readable, free to cite

Nearby counties in Washington

Grant · Grays Harbor · Island · Jefferson · Kitsap · Kittitas · Klickitat · Lewis

Look up a specific property

Our map shows each parcel in King County, Washington as septic, sewer, or unclassified, with the records we hold attached to the parcel.

Open the parcel map

Common questions

How do I get septic records for King County, Washington?

King County, Washington publishes onsite wastewater records through a county-built portal, searchable without an account. We hold 184,607 records for this county.

How many properties in King County, Washington are on septic?

Of the parcels we have classified in King County, Washington, 84,437 are on septic and 486,662 are on sewer. This counts parcels we have classified, not an estimate of the whole county.

Can I get a septic design for free?

Yes. You can generate and view a code-referenced septic design for a parcel at no cost: design flow from bedroom count, tank sizing, soil-driven drainfield area, dispersal method and setbacks. Where a recorded as-built exists for the property we start from it rather than from assumptions.

How is a septic system sized?

Design flow comes from the bedroom count under almost every state code, not square footage. That flow sets tank capacity, and the soil evaluation (percolation rate or soil profile, depth to water table and to any restrictive layer) sets the application rate and therefore the drainfield area.

What do I need before designing a septic system?

A soil and site evaluation, the design flow from bedroom count, the setbacks required to wells, property lines, surface water and foundations, and a reserve area for future replacement. On a lot with an existing permit, the original soil work is often already in the county record.

How often should a septic tank be pumped?

It depends on tank capacity and how many people use it, both of which are recorded on the system's as-built drawing. Pumping too rarely sends solids into the drainfield, which is the expensive failure. Pull the drawing to get your actual tank size rather than guessing.

Where is my septic tank and drainfield?

The as-built drawing filed with the county when the system was approved shows the tank location, the lid, and the drainfield footprint. That drawing is what a pumper or inspector needs, and locating a lid without it is billed as labor.

Do I need a permit to install or repair a septic system?

In almost all US counties yes: a permit before work starts, an inspection while the system is open, and a final as-built submitted at completion. That final drawing is what ends up in the county record.

Can I build over a septic drainfield?

No. Pools, sheds, driveways, fences and heavy vehicles over a drainfield destroy it, and the required setbacks are shown on the as-built drawing.

What is in a septic as-built drawing?

The tank location and capacity, the drainfield layout and size, the soil evaluation, and the approval date. It is the document a pumper, inspector or designer needs to work on the system.

Portal status and record counts on this page were last verified 2026-08-31.