It's a genuinely common question, especially for someone who's recently moved into a home and hasn't had a reason to think about it before. City sewer and septic systems handle the exact same job, getting wastewater away from your home, but they work in completely different ways, and the maintenance each one needs isn't interchangeable.
How City Sewer Works
On a city sewer connection, wastewater leaves your home through a single line that connects to the municipal sewer system, which carries it to a treatment facility. As a homeowner, your responsibility ends at the connection point to the city line, though you're still responsible for the condition of your own lateral, the pipe running from your house to that connection. There's no tank to maintain on your property, since the treatment happens off-site at a municipal facility.
How Septic Works
A septic system is entirely self-contained on your property. Wastewater flows into a septic tank buried in the yard, where solids settle and begin breaking down, while liquid effluent flows out into a drain field that filters it back into the soil. There's no municipal connection at all, which means all the maintenance responsibility sits with the homeowner, including periodic tank pumping to remove accumulated solids before they overflow into the drain field.
How To Tell Which One You Have
Check Your Utility Bill
A sewer utility charge on your water bill is the clearest sign you're on city sewer.
Look For A Septic Tank Lid Or Riser
A septic system typically has a visible access lid or riser somewhere in the yard, often a couple hundred feet from the house.
Check Your Property's Location
Homes within Kent's incorporated city limits are overwhelmingly on city sewer, while properties on the unincorporated edges of King County are more likely to be on septic.
Ask During A Home Purchase
This should be disclosed during a real estate transaction, and it's worth confirming directly if you're not sure from a past purchase.
Why It Actually Matters For Maintenance
If you're on city sewer, your main ongoing concern is the condition of your own lateral line, which can develop the same age-related issues as any other pipe, including root intrusion in an older clay or cast iron line. A camera inspection is the right tool to check that line's condition periodically, especially in an older home.
If you're on septic, the stakes are different and, in a real sense, higher for the homeowner, since skipping tank pumping is the single most common reason a septic system fails prematurely. This comes up regularly with Black Diamond properties on the edges of the incorporated city, where septic systems are genuinely more common than within Kent's own city limits.
What Actually Damages A Drain Field
A septic system's drain field does the real filtering work, and it's easy to damage without realizing it. Parking a vehicle over it compacts the soil in a way that reduces its ability to filter effluent properly. Planting trees with invasive root systems nearby risks the same kind of intrusion problem that affects sewer laterals, just underground in the drain field itself rather than in a pipe. Directing downspout or sump pump discharge onto the drain field adds water it wasn't designed to handle, shortening its working life.
None of this is obvious to someone who's never owned a septic system before, which is exactly why a lot of drain field problems trace back to an honest lack of awareness rather than neglect. If you've just moved into a septic property, it's worth having the system's condition and drain field location confirmed early, rather than finding out the hard way that a landscaping choice was working against the system.
What To Do If You're Genuinely Not Sure
If you've checked your utility bill, walked the yard looking for a tank lid, and you're still not certain which system you have, ask directly. The most reliable answer comes from your local water or sewer utility, who can confirm whether your address is connected to their system. If it isn't, you're on septic by default, and it's worth locating the tank and getting a baseline inspection scheduled rather than waiting for a problem to force the question.