Selling a House With a Septic System in Washington
Do you need a septic inspection to sell a house in Washington?
Yes - and the rules just changed. King County has required a certified inspection before title transfer for years, plus a recorded Notice of On-site Sewage System Operation and Maintenance Requirements. Snohomish County joins them on November 1, 2026 under Ordinance BOH26-02, and every remaining Washington county follows on February 1, 2027. The inspection can be done up to a year before closing, so the sellers who handle this early are the ones whose deals don't stall.
By Samantha Schlegel | September 17, 2026
Here's the call I don't want you to have to make.
It's day twenty-two. Your buyer's inspector pulled the lid on a tank nobody's looked at since 2011, the report came back with a saturated drainfield, and the buyer's lender just told them an FHA loan won't fund on a system in that condition. Now you're negotiating a five-figure repair from the weakest possible position - under contract, on the clock, with a buyer who has options.
Almost none of that was about the septic system. It was about when you found out.
And right now, timing matters more than usual. If your home sits in Edmonds, Mountlake Terrace, Brier, or unincorporated Snohomish County, a brand-new requirement takes effect November 1. If you're in Shoreline, Lake Forest Park, or North Seattle, the King County requirement has been on the books for years - and it's still the single most commonly missed step I see on septic listings.
What Your County Actually Requires
The rules differ depending on which side of the county line you're on. Both are about to converge.
King County - Shoreline, Lake Forest Park, North Seattle
If your property is served by an on-site sewage system, King County requires a certified on-site system maintainer to inspect it before title transfers. You schedule it. The maintainer files the report with Public Health – Seattle & King County, and their staff review it within ten business days. You can look up the filed report yourself at onlinerme.com under the property's application history.
There's a second step sellers miss constantly. Before closing, you must record a Notice of On-site Sewage System Operation and Maintenance Requirements - the OSSM - with the King County Recorder's Office. Your agent may know it as NWMLS form #22U. If a prior owner already recorded it, you're done; you don't record it twice. But you do have to hand the buyer a copy of the recorded notice before closing.
The inspection can be waived in a few narrow situations - a performance monitoring report filed by a licensed maintainer within the last six months on a regularly serviced system, new construction that's never been occupied with proof of vacancy, a newly permitted system whose first inspection isn't due yet, or a system that's been properly abandoned because the home connected to public sewer. Everything else gets inspected.
Lake Forest Park is worth a special note. The city extended sewer to most of its residences in a program that wrapped in 2008, but roughly 200 homes there still run on-site systems. Plenty of owners genuinely don't know which group they're in until the title report tells them.
Snohomish County - Edmonds, Mountlake Terrace, Lynnwood, Brier
This is the change. The Snohomish County Board of Health adopted Ordinance BOH26-02 on April 14, 2026, and it applies to properties closing on or after November 1, 2026. The program is called the Report of Property Transfer, and it has four steps:
Get the full system inspected by a certified septic professional. The inspection has to be within the past twelve months, and the tank must be pumped if the inspection calls for it.
Confirm the county has an as-built record of your system. If there isn't one on file, a certified contractor completes an On-Site Sewage System Site Plan instead.
Submit the Report of Property Transfer application. The fee is $245 for 2026 and 2027, rising to $255 after that. Review takes up to ten days, and an issued report is good for twelve months.
Give the required documents to your buyer.
Two exemptions worth knowing: systems installed within twelve months of the sale are exempt, and because inspections count for a full year, one you paid for last spring may already satisfy the requirement.
The county estimates about 2,785 septic properties change hands there each year, out of roughly 84,000 systems. Many are rural - but a substantial number sit inside ordinary residential neighborhoods in Lynnwood and Mukilteo, on streets where nobody thinks twice about it.
If your closing date lands anywhere near November 1, know which side of it you're on before you accept an offer. A home listed in mid-October in Edmonds is very likely to close under the new rules.
And this isn't a local quirk that might go away. Both counties are getting ahead of WAC 246-272A-0270, the state rule that makes property-transfer septic inspections mandatory in every Washington county starting February 1, 2027. King, Skagit, and Island counties were already there. The rest of the state is catching up.
The Part Sellers Get Wrong: The County Doesn't Make You Fix It
This is the most useful thing I can tell you, and it's the opposite of what most articles on this topic imply.
Neither county requires you to repair a failing system in order to sell. King County requires an inspection and a recorded notice. Snohomish requires an inspection and a filed report - and the ordinance says plainly that unresolved deficiencies simply carry forward to the buyer for follow-up. The health department's job is disclosure and a clean record, not forcing a repair before the deed changes hands.
So what actually forces the repair? Two things, and neither of them is the county.
Your buyer's lender. VA won't fund a home whose septic system isn't functional and free of public health hazards. FHA requires the system to be in working order at closing. If your buyer is using either - and in the $500,000 to $1,500,000 range around here, many are - a failed system stops being a negotiation and becomes a loan denial. Conventional appraisers can flag it too.
The inspection contingency. Once the condition is in a report your buyer is holding, you're renegotiating under a deadline. That dynamic is the same one I've written about with a failed sewer scope, just with a different pipe.
There's also a disclosure consequence that outlives the deal. Once you know a system is failing, that knowledge is yours permanently under the actual-knowledge standard on the Form 17 Seller Disclosure Statement. If the buyer walks, you disclose it to the next one. You can't unlearn it — which is exactly why finding out on your own schedule, with time to get bids, is worth so much more than finding out on theirs.
What It Costs and When to Start
Plan on $300 to $900 for the inspection itself, depending on system type and access, with pumping billed separately if it's needed. King County charges $216 to process the property transfer inspection report through OnlineRME; the buyer pays a separate operation and maintenance program fee at transfer. Snohomish's Report of Property Transfer fee is the $245 noted above.
If something's actually wrong, the range widens fast:
Minor repairs - pump, distribution box, root intrusion: $500 to $3,000
Drainfield replacement, conventional gravel-and-pipe: $8,000 to $15,000 typical, $5,000 to $20,000 overall
Mound and alternative systems: $15,000 to $30,000+
Full system replacement: $10,000 to $25,000+
Puget Sound labor sits at the high end of those national ranges, and King County requires a repair permit from Public Health before any work happens - which adds weeks, not days. There's help available if you need it: Craft3's Clean Water Loans cover design, permitting, and installation in King County, and Snohomish's Savvy Septic program offers rebates, grants, and guidance.
Start sixty to ninety days before you list. That's not padding. Between scheduling a certified maintainer, a possible pump, a ten-day agency review, tracking down an as-built or paying for a site plan, and recording the OSSM, the paperwork alone eats a month - and if the report turns up a problem, you want bids and options, not an ultimatum.
That timing pressure is sharper than it was a year ago. King County closed August 2026 with inventory up roughly a third year over year, months of supply climbing from 2.5 to 3.7, and only about 65% of homes selling within thirty days - down from 75% in July. In a market where buyers have choices, a two-week escrow delay doesn't cost you two weeks. It costs you the buyer.
This is the same principle behind every pre-listing decision I walk sellers through, whether it's unpermitted work, a buried oil tank, or a septic system: the problem you surface yourself is a line item, and the one your buyer surfaces is leverage.
Frequently Asked Questions
Does Snohomish County's new septic rule apply if I list before November 1, 2026?
What matters is your closing date, not your listing date. The Report of Property Transfer requirement applies to properties closing on or after November 1, 2026 - so a home listed in October that closes in December falls under the new rules. If you're listing this fall in Edmonds or Mountlake Terrace, plan for the requirement regardless.
Who pays for the septic inspection, the buyer or the seller?
In both King and Snohomish counties the property-transfer inspection is the seller's obligation, because it's tied to the transfer itself rather than to the buyer's due diligence. Your buyer may still order their own separate inspection under the inspection contingency. That's a different report with a different purpose, and it's normal.
Can I sell a house in Washington with a failing septic system?
Yes. Neither county conditions the sale on a repair - Snohomish explicitly allows unresolved deficiencies to carry forward to the buyer. The practical obstacle is financing: FHA and VA both require a functional system at closing, which narrows your buyer pool sharply and usually means a repair, a credit, or a price adjustment.
What if the county has no as-built record of my septic system?
That's common on older systems, and it's fixable. In Snohomish County, a certified septic contractor completes an On-Site Sewage System Site Plan and you submit it with your application. It takes time, though, which is another reason to check for the as-built early rather than assuming one exists.
How long is a septic inspection good for?
Up to twelve months in both counties. Snohomish accepts an inspection completed within a year of closing and issues a report valid for twelve months; King County's waiver path recognizes a performance monitoring report filed within the past six months on a regularly maintained system. If you had work done recently, pull the paperwork before you pay for a new inspection.
Before You List
A septic system is not a problem. An unknown septic system, discovered by someone else, on someone else's timeline, is a problem - and after November 1, there's one fewer place in this market where you can put that question off.
If you're weighing a sale in Shoreline, Edmonds, Mountlake Terrace, or anywhere in North King County, and you're not sure what's under your yard or what your county wants from you, that's a solvable question and a short conversation. I'm happy to walk you through the sequence and the timeline for your specific property. Reach out anytime.
About Samantha Schlegel
Samantha Schlegel is a residential listing specialist serving Shoreline and the greater Seattle area, with a focus on sellers navigating complex situations like probate, inherited homes, divorce, and relocation. She believes every seller deserves a strategy tailored to their real circumstances, not a one size fits all approach. Samantha works with Compass Real Estate and is known for guiding clients through tough transitions with clarity and care.
This article is general information about Washington real estate practice, not legal, tax, or engineering advice. County requirements and fees change — verify current rules with Public Health – Seattle & King County or the Snohomish County Health Department, and consult the appropriate professional for your situation.
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