What Is a Septic System and How It Works

One of the most important things to understand is this:

A septic system is not just a tank in the ground.

As Art Nikolin, General Manager of Septic Solutions LLC, explains it:

“A septic system is a series of filters. Your tank takes the brunt of the load, filters out most of it, then the system continues filtering further and further downstream.”

This concept changes everything.

When people think of a septic system as “just a tank,” they focus on whether water drains. When professionals look at a septic system, they look at how well each filter is protecting the next one, especially the final and most expensive filter of all: the drain field.

That perspective comes from decades of experience and a team holding 36 septic service licenses across inspection, design, and repair.

The septic tank is the first stage of treatment. Its job is to slow everything down.

When wastewater enters the tank:

• Heavy solids settle to the bottom as sludge
• Oils and grease float to the top as scum
• The clearer liquid layer in between moves on to the next component

This separation only works if water moves through the tank at the right pace.

Inside the tank, naturally occurring bacteria begin breaking down waste. But there’s an important balance at play. Septic systems are designed to treat human waste, not large volumes of food waste, grease, or chemicals.

As Art explains:

“There are different bacteria to break down waste. When you disrupt that balance by introducing large quantities of food waste, the balance is disrupted and one becomes dominant and it disrupts the entire system.”

The role of bacteria in septic systems is dependent on that balance and that is why introducing the wrong materials can disrupt treatment.
That disruption doesn’t stay in the tank. It carries forward.

And one thing is critical to understand: solids don’t disappear.

“You can liquefy them, but they don’t go away,” Art says. “All that does is push the problem further downstream.”

Depending on the site, soil conditions, and regulations, wastewater may pass through additional treatment components after the tank. These systems are designed to further reduce contaminants before effluent reaches the drain field.

In Washington State, these design decisions are not optional or aesthetic. They’re driven by:

• Soil type
• Groundwater depth
• Proximity to surface water
• Environmental protection requirements

Homeowners don’t choose system types the way they choose appliances. Designers do, based on what the land can safely support.

If the septic tank is the first filter, the drain field is the final one (and it’s the most vulnerable).

The drain field releases treated effluent into the soil, where it finishes filtering before re-entering groundwater. This process relies on:

• Oxygen
• Time
• Proper soil conditions

If you’re unfamiliar with exactly what a drainfield is and how it functions, it helps to understand why professionals treat it as the most critical and most fragile part of the entire system.

A biological layer called the biomat naturally forms in the drain field. When balanced, it helps regulate how quickly water moves into the soil. When overwhelmed, it becomes a barrier.

Art explains it simply: “Once that drain field is clogged, it’s done. It’s a single-use filter.”

This is why professionals are so focused on protecting the drain field. Replacing it is often the most expensive septic repair a homeowner can face.

Septic systems are designed for both waste strength and water volume.

The strength doesn’t change much. People still use soap, flush waste, and wash dishes. What does change is how quickly that waste moves through the system.

“If you’re using less water,” Art explains, “you’re giving solids more time to settle and break down. You’re reducing how much carries over into the drain field.”

Timing matters too.

Dumping an entire day’s worth of water use into a system over a two-hour window creates turbulence, stirs solids, and overwhelms downstream components. Slow, steady flow gives the system time to work as designed.

This is why simple habits such as spacing out laundry, fixing leaks,or using delay features on appliances  can significantly extend system life.

A septic alarm is not a nuisance. It’s information.

“Silencing the alarm doesn’t make the problem go away,” Art says. “It’s like putting tape over a check engine light.”

Alarms indicate a system state, often related to water levels or flow, not weather.

If an alarm activates during rain, that correlation is meaningful.

In many cases, alarms can be an early warning of hidden septic leaks or developing flow problems.

“Your system is designed to work rain or shine,” Art explains. “If rain triggers an alarm, something isn’t right.”

That “something” is often surface water intrusion, saturation, or a developing failure that needs attention.

Understanding how rainy weather affects septic systems is especially important in Washington, where prolonged wet periods are common.

Washington’s soil and rainfall patterns create challenges even in normal years.

Much of the state sits on glacial soils with dense clay layers. These layers slow vertical drainage, causing groundwater to build up horizontally during wet periods.
Septic systems are designed with this in mind. Problems arise when:

• Surface water is redirected toward system components
• Drain fields remain saturated for extended periods
• Floodwaters submerge system components

During flooding, systems may temporarily stop functioning not because they failed, but because hydraulic pressure reverses flow.

Once water recedes, most systems recover on their own. Inspections afterward help confirm nothing shifted or sustained damage.

However, it’s important to recognize that the challenges posed by Washington's unique weather conditions, like saturated drain fields and redirected surface water, can also impact system performance. 

Regular inspections ensure any potential issues are identified and addressed before they cause long-term damage.

Maintenance isn’t about selling service. It’s about protecting a system’s lifespan.

Washington homeowners can also reference the Washington State Department of Health’s official guidance on caring for your septic system, which aligns closely with the inspection and maintenance practices required by state law and agreed upon by professionals.

Art often compares septic systems to vehicles:

“You don’t just drive a car forever without maintenance. You keep records. Septic systems are no different.”

Many system failures can be traced back to a handful of avoidable behaviors outlined in our blog about the top mistakes in septic system maintenance.
Annual inspections and regular pumping:

• Reduce stress on the drain field
• Catch small issues early
• Preserve documentation for resale

Neglect doesn’t cause immediate failure. It quietly shortens lifespan.

We’ve seen firsthand how delayed maintenance accelerates failure. Read a case here involving a system installed in 1974.

This belief is one of the most persistent septic system myths and one of the most damaging.

Septic systems fail silently.

By the time symptoms appear, damage is often already done. That’s why homeowners and professionals work best as a team.

“You live there day in and day out,” Art says. “You’re actually in the best position to notice small changes.”

When homeowners track water use, pay attention to alarms, and work with qualified professionals, systems last longer and fail less often.

Septic systems don’t just serve individual properties. They protect:

• Groundwater
• Streams and rivers
• Estuaries - like the Puget Sound
• Public health

Every properly maintained system is a small contribution to protecting Washington’s environment.

Understanding how your septic system works isn’t about becoming an expert. It’s about knowing enough to make good decisions before problems surface.
That knowledge is one of the most valuable tools a homeowner can have.