A sewer backup is one of those surprises that can derail a weekend and a renovation budget. If you own in The Lakes on Mercer Island or you are preparing to sell, understanding your side sewer can save you time, stress, and money. In this guide, you will learn what a side sewer is, who maintains it, what you can and cannot connect, how to spot early warning signs, and the steps to take for permits, inspections, and repairs. Let’s dive in.
Side sewer basics
Your side sewer, also called a private sewer lateral, is the pipe that carries wastewater from your home to the public sewer main. It typically includes the building sewer inside or immediately outside the foundation, any exterior cleanouts, and the lateral pipe that runs to the connection point with the public main. That last connection is often a wye or tap.
Knowing where your side sewer runs and where it connects to the public system helps you plan maintenance, protect landscaping, and respond fast in an emergency.
Who owns what
In most local systems, including municipalities in King County, the property owner is responsible for the private side sewer from the house to the point it connects with the public main. The city or county maintains the public mains and manholes.
Ownership lines can vary by jurisdiction. On Mercer Island, confirm the exact boundary with the City of Mercer Island Public Works because some cities define it at the property line while others use the actual tap on the main. This affects who pays for repairs, which permits you need, and who to call during a backup.
Mercer Island permits and codes
Side sewer work touches plumbing, excavation, and sometimes the public right of way. Plan for:
- Building or plumbing permit for replacement, extensions, or major repairs.
- Public Works or right of way permit if you disturb streets, sidewalks, or the planting strip. A traffic control plan may be required.
- Inspections that can include in-ground checks, pressure or leak tests, and CCTV confirmation before final sign-off.
- Licensed contractor requirements. Most jurisdictions restrict DIY for laterals and require a licensed plumber or contractor to perform the work.
The Washington State Plumbing Code applies with local Mercer Island amendments. The City manages local standards for sewer work, permits, and restoration. Some Washington cities require a lateral inspection at sale or during major remodels. If you are selling or renovating, ask City staff whether Mercer Island has any sale-time inspection or disclosure rules for laterals.
The Lakes layouts and risks
The Lakes features mid-sized and waterfront lots, mature trees, and some slopes. These site traits affect side sewer length and exposure.
- Longer laterals and slopes increase the chances of settling, offsets, and root entry.
- Mature trees raise the risk of root intrusion, especially in older clay or cast-iron lines.
- Aging materials are more likely to crack, separate at joints, or collapse compared to modern PVC or HDPE.
If your home is older or has extensive tree cover, proactive inspection is a smart move.
Warning signs to act on
Catching problems early can prevent a backup. Watch for:
- Slow drains in more than one fixture.
- Gurgling toilets when other fixtures run.
- Sewage odors in a basement, crawlspace, or yard.
- Backups that coincide with heavy rain, which can point to stormwater inflow or infiltration.
- Wet, spongy ground along the lateral path.
- A sudden jump in your water or sewer bill.
What not to connect
Keeping stormwater and debris out of your side sewer protects your line and the regional system.
- Never connect roof downspouts, yard or driveway drains, or sump pumps to the sanitary sewer. These must discharge to approved storm systems per local code.
- Do not pour fats, oils, or grease down drains. Collect and dispose of them with solid waste.
- Do not flush wipes, diapers, sanitary products, cotton swabs, or paper towels. Use the “only toilet paper” rule.
- Avoid discharging solvents, paints, pesticides, or motor oil. These are regulated and can harm treatment processes.
- Use garbage disposals lightly and avoid fibrous foods and grease.
- Appliance discharges like water softeners are often allowed, but rules vary. Confirm with the City of Mercer Island.
Maintenance that pays off
A bit of routine care can extend the life of your lateral and reduce emergency calls.
- Locate your cleanouts and map the likely path of the line to the street.
- Schedule periodic CCTV inspections, especially if your line is older or you have large trees.
- Clear roots and grease buildup with professional hydro-jetting as recommended by your plumber.
- Use drain strainers and train household members on what not to flush.
- Manage landscaping near the route. Root barriers or choosing less aggressive species can help.
When to get a camera inspection
A camera inspection gives you a clear view of hidden issues and is worth the modest upfront cost in several cases:
- Recurring backups or slow drains.
- Before buying or selling a property in The Lakes.
- After heavy construction or major landscaping that could disturb the soil.
- If your lateral is about 25 to 40 years old or older, depending on materials and condition.
A CCTV video can reveal cracks, offsets, root intrusion, and any illegal storm connections.
Repair options to consider
The right fix depends on the location, length, material, and severity of damage.
- Spot repairs can address isolated defects.
- Full replacement may be best for extensive damage or very old materials.
- Trenchless methods such as pipe bursting or cured-in-place pipe lining can minimize yard and hardscape disruption. Your contractor will evaluate soil conditions, tree cover, and pipe layout to recommend the best method.
Keep inspection reports and permits for your records. These documents support future disclosures and can streamline a sale.
Hiring and permits checklist
Choose experienced pros and keep the process organized.
- Hire a licensed plumber or contractor with local side sewer experience on Mercer Island.
- Confirm the contractor will pull all required permits and coordinate right of way work with the City.
- Request proof of insurance and recent references.
- Ask for a written scope, timeline, and method of repair.
- Schedule required inspections and retain all approval documents.
Buying or selling in The Lakes
Side sewer clarity protects both parties and reduces last-minute surprises.
- Sellers should disclose known sewer issues as required by state rules.
- Buyers should request past permits, repair invoices, and any camera reports. You can also ask the City for permit file history.
- Consider a lateral inspection contingency for older homes so you understand repair needs and budget.
- If inspections reveal defects, buyers and sellers can negotiate repairs, price adjustments, or escrow holds. City permits and approvals may be required before work or transfer depending on scope.
Emergency steps
If sewage backs up into your home, act fast.
- Stop using water immediately.
- Call a licensed plumber experienced with laterals and, if applicable, pump systems.
- If you suspect a public main issue, such as multiple homes affected or an overflowing street manhole, notify the City of Mercer Island Public Works or the local non-emergency line.
- For environmental spills or public health hazards, regional agencies may also need to be notified.
Plan your next steps
Side sewer upkeep is part of owning in The Lakes, and a little diligence goes a long way. Whether you are preparing to list, evaluating a purchase, or planning renovations, having current inspections and permit records strengthens your position and reduces risk.
If you would like a coordinated plan that aligns sewer due diligence with your real estate timeline, reach out to Unknown Company. Request Your Private Home Valuation and tap our vetted contractor network to keep your move on track.
FAQs
Who pays for side sewer repairs on Mercer Island?
- In most cases the property owner pays to maintain and repair the side sewer from the home to the connection with the public main. Confirm the ownership boundary with the City of Mercer Island.
Do I need a permit to replace my lateral in The Lakes?
- Yes. Lateral replacement or major repairs typically require building or plumbing permits and possibly a right of way permit if work extends into the street.
Are sump pumps allowed to discharge to the sanitary sewer?
- Generally no. Sump pumps, downspouts, and yard drains must not connect to the sanitary sewer. Ask the City for approved stormwater discharge options.
How often should I schedule a camera inspection?
- For older systems or if you have recurring issues, inspect before a sale or every few years. Otherwise, a preventive inspection every 5 to 10 years is common, adjusted for pipe age and tree proximity.
Can I prevent tree roots from returning after clearing?
- You can reduce recurrence with root barriers, trenchless lining, or full replacement using modern materials. In some cases removing problematic trees may be the most reliable long-term fix.
