What Happens to Your Septic System When You Sell a Home in Redmond, WA?

Do you need a septic inspection to sell a home in Redmond, Washington?
Yes. Because Redmond is in King County, a licensed On-Site System Maintainer (OSM) inspection is required before the transfer of title — and any deficiencies found must be disclosed to the buyer.

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I have a client in Redmond who really, really does not want anything to do with her septic system. She can’t see it. She doesn’t want to smell it. It exists underground and, as far as she’s concerned, it should stay there.

The problem? Her septic tank has no visible lid or access cap on the surface of her lawn — it’s completely buried. So every time it needs to be pumped, she has to dig up a section of her grass to let the service company in, and then put everything back together afterward.

She was getting ready to list her home, and the last thing she wanted was a freshly excavated hole in the yard right before listing photos and buyer showings. So she started pushing back the required pre-sale septic inspection, hoping to schedule it a couple weeks after going live on the market.

Here’s the thing though — while her septic had been inspected about 15 months ago and she knew it was in good shape, King County now requires the inspection to be valid within 12 months of the title transfer. Her previous inspection had just barely aged out. She needed a new one.

To complicate things further, I mentioned that another client of mine — down in Normandy Park — had recently spent about $400 to install a permanent access riser (sometimes called a “port”) that brings the lid up to ground level. No more digging. Future pumpers and inspectors could just walk up and pop it open. He thought it was a great investment for the new buyers, and he was right.

My Redmond seller’s reaction? A hard no. She wasn’t interested in making access easier to a thing she didn’t want to think about. Which is totally fair — but it did send us down a rabbit hole of figuring out what was actually required versus what was just a good idea.

Here’s what we learned.

King County Requires a Septic Inspection Before Every Home Sale

If your Redmond home has an on-site sewage system — the technical term for a septic system — King County Public Health requires that a licensed On-Site System Maintainer (OSM) inspect the system and file a report before title transfers to a new owner.

This is not optional, and it’s not something you can negotiate around in the purchase and sale agreement. The inspection must happen.

As of April 2025, King County updated its code to extend the validity window for these inspections. An inspection is now good for 12 months before a property sale, up from the previous 6-month window. If you’ve had an inspection within the past year, you may be able to use it — but confirm the exact date, because a week or two can matter.

What the Inspector Is Actually Looking For

The OSM’s job isn’t to find reasons to fail your system. The inspection is fundamentally about disclosure — it identifies any deficiencies and puts them on record so the buyer knows exactly what they’re getting.

During the inspection, a licensed OSM will typically assess:

• Whether the tank is functioning properly (flow in, flow out, no signs of failure)
• Scum and sludge levels — which determines whether the tank needs to be pumped
• The condition of the baffles and any mechanical components
• The lid and access point condition
• The drainfield — looking for signs of saturation or failure
• Whether an accurate as-built drawing exists in King County’s records

That last one matters: King County requires an as-built diagram of the system to be on file. If one doesn’t exist, the OSM will need to create one — which adds cost, sometimes $300–$500 extra.

So What About the Lid?

Here’s the question that sent my client and me into research mode.

A septic tank that’s fully buried with no accessible lid isn’t unusual in older Redmond homes — many systems installed in the 1960s through 1980s were simply buried without surface access. Over time, industry standards have evolved, and newer systems are typically installed with risers that bring the access point up to ground level.

Under King County code, replacing or adding a sewage tank lid falls under the definition of a “limited repair” — meaning it’s a relatively minor fix that doesn’t require a full repair permit or a licensed master installer. A lid replacement can typically be handled by the OSM company directly.

However — and this is important — a missing or non-watertight lid is not automatically a deal-breaker. It will show up as a deficiency on the inspection report, but King County’s time-of-sale inspection process is designed to disclose deficiencies to buyers, not necessarily mandate that every one of them be corrected by the seller before closing. The seller and buyer negotiate who handles what.

That said, a watertight lid is a real code requirement under Washington State’s septic system standards, so don’t expect a buyer (or their lender) to shrug it off entirely.

Do You Have to Install an Access Riser?

This is the specific question my Redmond seller wanted answered: is she required to install a surface-level access port as a condition of sale?

The short answer is no — not as a mandatory condition of the King County time-of-sale inspection process.

However, there’s a practical reality here worth understanding. If the OSM can’t easily access the tank to perform the inspection, someone is going to need to dig. That’s true whether you have a riser or not. The inspection can’t happen without access.

And if the inspection flags the lid condition as a deficiency — which it likely will if the lid isn’t watertight or is difficult to access — that goes into the report that gets filed with King County and disclosed to the buyer.

Installing a riser isn’t a code requirement for the sale, but it’s worth understanding what you’re trading off. A buried system with a non-compliant lid disclosed to buyers can raise questions, invite further negotiation, or give a cautious buyer pause — especially on the Eastside where buyers often scrutinize every line of the inspection report.

At around $400 in many cases, a riser installation is one of the lower-cost pre-listing upgrades available. But it’s your call.

A Few Other Things to Know About Selling with Septic in Redmond

Pumping is not automatically required. A common misconception is that you must pump the tank before listing. Pumping is only required if the inspector determines the tank levels make it impossible to properly assess the system. You won’t know until the inspection happens.

You don’t need to bring the system up to current code. The inspection is a disclosure process, not a full code-compliance review. Your system doesn’t need to be brand new — it needs to be functional and disclosed.

Watch out for upsell pressure. Some service providers will imply that risers, filters, or other upgrades are required by King County for the sale. In most cases, they are not required — they may be recommended, but that’s different. Ask your OSM to be specific about what is a code requirement versus what is optional.

The 22U notice is required at closing. Separately from the inspection, King County sellers must record a Notice of On-Site Sewage System Operation and Maintenance Requirements (NWMLS Form 22U) at the King County Recorder’s Office before closing. If it’s already on title, you’re done. If not, your escrow company will typically handle it.

FAQ: Septic Systems and Home Sales in Redmond, WA

Can I sell my Redmond home if the septic inspection reveals a deficiency?

Yes, in most cases. The inspection is designed to disclose deficiencies, not automatically block a sale. You and the buyer can negotiate who addresses each item — the seller may fix it, the buyer may accept it as-is, or you may split the cost. Major structural failures to the tank or drainfield are a different situation and may require permits and licensed installers to repair.

How long is a septic inspection valid when selling a home in King County?

As of April 2025, King County extended the validity window to 12 months before title transfer, up from the previous 6 months. If your system was inspected within the past year, confirm the exact date with your OSM to see if it qualifies.

What does a King County time-of-sale septic inspection cost?

Costs vary depending on the size and complexity of your system, but most sellers budget $300–$900 for the inspection itself. Additional costs may include pumping (if needed), an as-built drawing (if King County doesn’t have one on file, typically $300–$500 extra), and the county filing fee. Your OSM can give you a more accurate estimate based on your specific property.

The Bottom Line

Selling a home with a septic system in Redmond isn’t complicated — but it does require some planning. Get the inspection scheduled early so you know what you’re dealing with before you’re in the middle of negotiations. Understand that deficiencies go into a report that the buyer will see. And know that some things that get flagged are negotiable, not deal-breakers.

As for my client with the buried tank and the immovable stance on access risers — we figured out a plan. The inspection will happen after listing, within the allowable window. The deficiencies, if any, will be disclosed. And if the new buyers want a riser installed, that’ll be a conversation at the negotiating table.

Every situation is different, and that’s kind of the point. There’s no universal answer — just a framework, and someone who knows how to apply it.

If you’re getting ready to sell a home in Redmond or anywhere on the Eastside and you have a septic system, I’m happy to walk you through what to expect. Text HOME to 206-245-8813 and I’ll respond directly — or visit HomeProAssociates.com to learn more.

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Emily Cressey is a REALTOR®, Broker, and Team Lead at HomePro Associates, affiliated with Keller Williams Greater Seattle. She serves buyers, sellers, and investors throughout King and Snohomish counties, Washington State. WA Real Estate License #20109399.