Septic System 101 – Gravity vs. Pumped Septic Systems: What’s the Difference?

Tall grasses.

If you are buying a home with a septic system, you may hear terms like gravity system, pump chamber, or pumped system. The differences sound complicated, but the basic idea is pretty simple.

A Conventional Gravity System

A gravity system is the simplest type.

Wastewater from the house flows into the septic tank. Solids remain in the tank while the liquid wastewater, called effluent, flows out toward the drainfield.

As the name suggests, gravity does the work. The property has enough natural slope for the effluent to travel from the septic tank to the drainfield without a pump.

Once it reaches the drainfield, the effluent is distributed through underground pipes and gradually filters into the soil.

What Is a Pumped Septic System?

Sometimes the drainfield cannot be located downhill from the septic tank, or the design of the system requires the effluent to be distributed differently.

That’s where a pump comes in.

A pumped system typically has a pump chamber in addition to the septic tank. Effluent flows into the chamber and is held there until it reaches a certain level. A pump then sends it to the drainfield.

Think of it as giving the wastewater a little help getting where it needs to go.

What About At Grade Drainfields?

Some properties on the Mendocino Coast have systems where the drainfield is constructed at or near the natural ground surface rather than entirely below ground.

These systems may use a pump to move and distribute effluent to the drainfield.

The type of septic system used for a particular property depends on factors such as the soil, slope, groundwater conditions and the original system design.

Is One Better Than the Other?

Not necessarily.

A gravity system is mechanically simpler because it doesn’t depend on a pump. A pumped system has additional equipment that needs to be maintained, but it can allow a septic system to work on a property where a conventional gravity design may not be appropriate.

If you are buying a home with a pumped system, it is helpful to understand where the pump chamber is located, how the system operates, whether it has an alarm, and what maintenance has been performed.

The important thing isn’t whether the property has a gravity or pumped system. It is knowing what type of system you have and whether it is functioning properly.