What an on-site sewage system is, and who regulates it
Outside the sewer service areas, much Eastside and north King County housing runs on an on-site sewage system (OSS): a septic tank, a distribution box or pump chamber, and a drainfield in the yard where soil finishes treating the wastewater. Parts of Woodinville, Sammamish, Issaquah, and most rural King and Snohomish county parcels are on septic. Form 22D paragraph 4 (Utilities) and the seller's Form 17 disclosure state whether the home is connected to a public sewer main or a septic tank.
The Washington State Department of Health sets the statewide rule in WAC 246-272A; local health jurisdictions administer it: Public Health Seattle & King County under the King County Board of Health Code, Title 13, and the Snohomish County Health Department (formerly the Snohomish Health District). Both license or certify the professionals who design, install, inspect and pump systems; in King County the inspector at time of sale must be a licensed on-site system maintainer (OSM).
Form 35 paragraph 9 says OSS systems are subject to strict governmental regulation and occasional malfunction and even failure, and points you to Form 22S. Your general home inspection does not evaluate the system beyond the line from the house to the tank (Form 35 paragraph 1(a)). That is why septic has its own addendum and its own clock.
King County's time-of-sale requirement, and Snohomish County
King County Board of Health Code § 13.60.030 requires that before an OSS-served property transfers, a licensed on-site system maintainer inspect the system and file an Operation and Maintenance Report (O&M Report). Form 22S-King writes it into the contract. Paragraph 3(a): the seller retains the OSM and delivers the O&M Report to you when complete. Paragraph 3(b): the contingency is deemed waived unless you give notice of disapproval within the days written (5 if blank) after receipt; timely disapproval terminates with your earnest money refunded.
Paragraph 3(c) adds the county paperwork: the seller's Form 22U notice of operation and maintenance requirements, recorded before closing; your Form 22V receipt, signed on or before closing; and the county's O&M Program Fee. Paragraph 4, if checked, adds a separate inspection-and-pumping contingency with its own deadlines on the form. The advisory: no pumping before the O&M Report; the system must be observed first.
Snohomish County has no county-specific addendum. Form 22S governs: the seller has the OSS inspected (pumped if needed), delivers the report within the days written (10 if blank) after mutual acceptance, and you have the days written (5 if blank) after receipt to disapprove. Its paragraph 4 requires the seller to comply with local pre-sale inspection ordinances; we confirm the Snohomish County Health Department's requirements when the file opens.
What the inspection covers, and who pays
The maintainer uses the county as-built to locate the tank, distribution box, pump chamber and drainfield, then opens the tank lids. Inside: the liquid level relative to the outlet (above it means the drainfield is not accepting effluent), the depth of scum and sludge, the condition of the inlet and outlet baffles or effluent filter, and signs of cracks, root intrusion or leaks. On a pressure or proprietary system: the pump, floats, control panel and alarm. At the drainfield: soggy ground, surfacing effluent, odors or unusually lush growth, and standing liquid in the monitoring ports. Water is run from the house to watch flow. Pumping follows if the solids call for it.
The result is a written report: components, condition, deficiencies, recommendations, whether the tank was pumped, and in King County the O&M Report filed with Public Health. Read the deficiencies and recommendations line by line.
Who orders and pays is as written in the contract. Under Form 22S-King paragraph 3 the seller retains the OSM for the county report; under Form 22S paragraph 5 and 22S-King paragraph 4 the seller pays for inspection and pumping. A prior inspection within the months written (12 if blank) can satisfy the pumping contingency. Anything beyond that is yours to order and pay for; your lender may add requirements.
Red flags, and what happens if the system fails
Some findings are routine (a tank due for pumping, a cracked riser lid, a filter to clean). Others deserve a conversation with your agent before your window closes:
- Effluent surfacing or soggy ground over the drainfield, sewage odors outdoors, or a strip of grass far greener than the rest of the yard.
- Slow drains, gurgling or backups inside the house, or a high-water alarm that has been silenced.
- Liquid in the tank above the outlet invert, or standing liquid in the drainfield monitoring ports.
- Missing or deteriorated baffles, a cracked or leaking tank, or roots inside the tank or lines.
- No as-built on file with the county, components that do not match the as-built, or bedrooms added beyond what the system was designed and permitted for.
- A drainfield inside the required setbacks to a well, stream or property line, or a reserve drainfield area that has been built over or paved.
Records, the recorded notice, and maintenance after you own it
Public Health Seattle & King County keeps OSS records by parcel: as-built drawings, permits, prior O&M Reports and repair history, searchable online by address or parcel number. Our transaction administrator pulls them at file open. The Snohomish County Health Department maintains equivalent records for its parcels. If no as-built exists, the seller's Form 17 and maintenance records are what you have, and the report should say the system was located by probing.
In King County the Form 22U notice recorded before closing puts the operation and maintenance requirements on title, and they become yours: measure sludge and scum at least every three years for a home without a garbage disposal and annually with one; have performance inspections every three years on a gravity system and annually on pressure distribution, mound, sand filter, aerobic and other proprietary systems, with a maintenance contract where required; pump when the inspection calls for it; keep records.
Day to day: keep vehicles, structures and deep-rooted trees off the tank and drainfield, spread laundry loads, fix leaks, keep grease, wipes and chemicals out of the drains, and know where the reserve area is before you plan a shop, pool or addition. Repairs need a county permit and usually a licensed designer, and range from a filter to a full new drainfield, so learn the system now.
Your checklist
- 1Confirm from Form 22D paragraph 4 and the Form 17 that the home is on an OSS, and note which septic addendum is attached: 22S-King, 22S, or a county form.
- 2Read the addendum for the seller's report deadline and your disapproval window; note whether the Form 22S-King paragraph 4 pumping contingency is checked.
- 3Ask our transaction administrator for the county as-built and prior O&M Reports at file open, and compare the drawing to the property.
- 4If the buyer's-right-to-attend box is checked, plan to be there; you will learn where everything is and what the alarm means.
- 5Read the O&M Report and inspection report line by line: deficiencies, recommendations, whether pumping was done, and the maintainer's overall finding.
- 6Send anything on the red-flag list to your agent the day you receive the report; a specialist opinion or a repair proposal takes time.
- 7Decide before your window ends: proceed, propose terms by addendum, or deliver written disapproval.
- 8In King County, sign the Form 22V receipt at or before closing and expect the program fee on your settlement statement.
What RexMont tracks for you
- We identify the septic addendum on the file at open, log the seller's report deadline and confirm the OSM is scheduled; a late report delays your clock but not your closing date, so we chase it early.
- We compute your disapproval window from the day the report is delivered to you under Form 21 General Terms k and l, and send you the deadline.
- We pull the county as-built and prior O&M Reports and compare bedroom count and components to the listing, then flag mismatches to your agent.
- In King County we confirm the Form 22U notice is recorded (with a recording number) before closing, that Form 22V is signed, and that the program fee appears on the settlement statement.
- We check that no pumping was done before the O&M Report was performed, per the Form 22S-King advisory, and raise it with the listing side if the dates suggest otherwise.
Jennifer Johansen, RexMont’s transaction administrator, coordinates every date and document from mutual acceptance to keys. Questions on price, terms, or strategy go to your RexMont agent.
Sources
- Public Health Seattle & King County — on-site sewage systems program and records
- Snohomish County Health Department (formerly Snohomish Health District) — on-site sewage
- Washington State Department of Health — on-site sewage systems
- WAC 246-272A — On-site sewage systems (Washington rule)
- Northwest Multiple Listing Service — standard forms (Form 22S, 22S-King, 22U, 22V, 35)
This guide explains the process and the standard NWMLS forms in general terms. It is not legal, tax, or lending advice, and your contract controls. Talk to your RexMont agent, escrow officer, lender, or attorney about your specific situation.
