Gravity Septic System
A gravity septic system is the most common and affordable option for residential properties. Using natural downhill flow, wastewater moves from the septic tank into the drainfield, where soil safely filters and cleans it before it reaches the water table.
Gravity Septic System at McNair Septic
A conventional gravity system is the simplest and often cheapest septic system available. This system consists of a septic tank and a drainfield (AKA leech field). The septic tank must be placed accordingly so that it is downhill from the home/building’s plumbing. A bio-microbial process in the septic tank treats the waste before it reaches the drainfield. As the septic tank fills, effluent leaves through an outlet and is transported by gravity to the drainfield. The effluent is then dispersed by a distribution box into several lateral lines where it is filtered through the soil. By the time the effluent has filtered through the soil and reached the water table, it is clean.
A pump will be incorporated into the system if gravity flow cannot be used to transport effluent from the septic tank to the drainfield. This can be done multiple ways depending on site conditions. Systems that include pumps will also include high-water alarms which will go off if the system begins to back up.
Gravity systems should have an operation and maintenance inspection done every three years of operation. Concurring reports may need to be turned in to the county.
Septic systems are sized according to the amount of waste they will be treating, usually estimated by the number of bedrooms in the home. For non-residential buildings, water usage usually determines the size.
The most basic drainfields include parallel, 60-foot-long lateral lines that are spaced six to eight feet on center. More intricately designed drainfields may include lateral lines of varying lengths (from 36 to 60 feet) that branch out from the distribution box in multiple directions.
Upon installation, the only parts of the system that will be visible from above ground are 24-inch riser lids above the tank, a distribution box lid, and observation port lids at the ends of the lateral lines. Each of these lids will be flush with the final grade and can be walked on, mowed over or disguised to lessen noticeability.
Drainfields should be treated as fragile to increase their longevity. Large animals such as cows or horses should not be kept on drainfields and vehicles should not be driven over them. Vegetation with intrusive roots should not be planted near them. Finally, a home owner should be mindful of what is going into the system.
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FAQs About Gravity Septic Systems
What is a gravity septic system?
A gravity septic system is the simplest type of system, consisting of a septic tank and a drainfield. Wastewater flows naturally downhill from the tank to the drainfield, where the soil filters and cleans it before reaching groundwater.
Do all gravity systems need a pump?
No, many gravity systems rely solely on natural flow. However, if the property’s slope doesn’t allow for gravity flow, a pump is added along with a high-water alarm to prevent backups.
How often should a gravity system be inspected?
Gravity systems should be professionally inspected every three years. Some counties may also require reports to be filed with local health departments.
What size gravity septic system do I need?
System size is typically based on the number of bedrooms in a home. For commercial or non-residential buildings, sizing is determined by estimated water usage.
What should I avoid with a gravity system?
To protect your drainfield, avoid driving vehicles over it, keeping large animals like cows or horses on it, or planting trees and shrubs with invasive roots nearby.
The Process
Planning
All we need is your parcel number or address to begin. We research your property in advance, gather details about your future plans, and may schedule a site visit or call. Any questions are addressed quickly to keep the process moving.
Soils Evaluation
Most projects start with a soil evaluation (perc test), the first step toward system approval. We handle everything—from digging and testing to county applications, fees, and paperwork—while keeping you updated every step of the way.
On-Site Septic System Design
After completing the soil evaluation, we quickly create a detailed, cost-effective septic design, typically within one to two weeks, that includes all calculations, maps, and specifications, while handling every detail of the submittal process for you.
Review and Permitting
Most counties allow up to three weeks to review septic designs and soil evaluations, though some return them sooner. Once approved, we’ll send you a copy and can also forward it to licensed installers so you can receive system bids.
Taking Care of You
We handle everything—even the required county as-built map—so your septic system is approved and recorded. With no complex contracts, we start right away and keep things moving. Consultations are always free, so call us anytime.
Support
We can assist you in finding reputable septic installation and maintenance companies that can service and maintain your new system.
