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Septic Systems: What You Need to Know

Buying or building a property in Northern Minnesota or Northern Wisconsin typically means dealing with a septic system. They’re a regular part of life in the great Northwoods. If you’re not familiar with septic systems, here’s a quick overview as well as a guide to the three basic designs. 

What is a septic system?

A septic system is a wastewater treatment system for properties not served by a municipal sewer. They generally consist of one or more septic tanks and a drain field which provides biological treatment of the wastewater before it is introduced back into the soil.  

The type of septic system put in place is determined a variety of factors, including the site conditions, soil type, depth to the seasonal high water table, and the size of the home. Building code requires septic systems to be setback from water bodies, roads, and trees, so that is another factor influencing the design. 

Approximately 25% of households in the U.S. are served by a septic system.

Types of septic systems

Holding tank 

A holding tank is simply a septic tank without a drain field. Wastewater generated by a home or cabin flows into the tank until an alarm indicates the tank is full and needs to be pumped. Since there is no drain field, waiting to pump the tank could cause a backup into your home, so it’s important to have a good working relationship with a septic system maintainer who can pump your tank in a timely manner.

Gravity system 

A gravity septic system—commonly referred to as a conventional or in-ground system—consists of a septic tank and a gravity-flow trench drain field system. Solids in the wastewater are separated in the septic tank. Gravity then causes the gray water to flow into a distribution box or a series of drop boxes which distributes the gray water into the trenches. Most trench systems are built to fill one trench at a time. Once one trench is full, the gray water overflows into the next trench in line. 

Gravity systems still require pumping to get the solids out, typically every three to five years.  

Pressurized bed system

Pressurized systems are used when soils are suitable for an in-ground system, but gravity flow cannot be achieved due to elevations or other site restrictions. These systems utilize a pump and a separate tank after the septic tank to dose the liquid waste to a drain field. The drain field is generally rectangular in shape and includes a series of three to six small-diameter pipes with perforations called laterals. These lateral pipes are all connected to the “pump dose line.” When the pump turns on, the lateral system is pressurized, dispersing the liquid waste evenly throughout the drain field area.  

Further reading on septic systems

With septic systems, a little knowledge of their operation goes a long way toward helping you feel comfortable. If you’d like to know more about septic systems and their maintenance, check out this excellent guide.


Brian Koski
Owner, Septic Check, Milaca, MN