Septic Tank or Holding Tank: The Difference
These two get confused constantly, including by people who already own one. They look similar, they are often made by the same manufacturer in the same material, and they do completely different jobs.
A septic tank treats and discharges
Solids settle, and the liquid flows out to a drain field where soil and microbes finish the treatment. It is one part of a wider onsite system. Because effluent reaches the ground, septic tanks are permitted products and approval requirements apply.
A holding tank stores only
Nothing discharges. Everything stays in the tank until a pump truck removes it. There is no drain field and no treatment, which is exactly why a holding tank works on sites where a drain field is impossible.
The short version: a septic tank is part of a treatment system, a holding tank is a sealed container on a pump-out schedule.
When a Holding Tank Is the Right Choice
Holding tanks are usually chosen because a drain field is not an option, not because someone prefers them.
- No room for a drain field. Small lots, steep ground, or setbacks from wells and property lines that leave nowhere to put one
- Unsuitable soil or a high water table. Ground that cannot absorb effluent, or groundwater too close to the surface for dispersal to be safe
- Seasonal or intermittent use. Cabins, hunting camps and vacation properties where flow is too irregular for a treatment system to work well
- Temporary sites. Jobsite trailers, construction sites and events, where the facility exists for months rather than decades
- A failed system with no room to replace it. Sometimes a holding tank is the only permitted option left
The thing most buyers underestimate
A holding tank does not reduce the volume it receives. Every gallon that goes in has to be pumped back out, so the tank fills at exactly the rate the property produces wastewater.
Before you choose a size, estimate the gallons per day the property will actually use and divide the tank capacity by that number. That tells you roughly how often a pump truck has to visit, and pumping frequency is the real running cost of a holding tank rather than the tank itself.
Full time occupancy fills a tank far faster than most people expect. Seasonal and jobsite use is where holding tanks make the most sense.
Sizing a Holding Tank
Sizing works differently from a septic tank. A septic tank is sized to hold and settle a few days of flow. A holding tank is sized to set an acceptable interval between pump-outs.
Two questions decide it. How many gallons a day will the property produce, and how often are you willing to schedule a truck? A larger tank costs more up front and reduces visits. A smaller tank costs less and fills sooner.
We stock holding tanks from 300 gallons up to 1,500 gallons, in standard and heavy duty builds. For applications beyond 1,500 gallons, contact our sales team and we will size it with you.
Permits and Local Requirements
Holding tanks are regulated, and the rules are set locally. Some jurisdictions restrict them to specific situations rather than allowing them as a general alternative to a septic system. Many require a high level alarm so the tank is not overfilled between visits, and some require a service contract with a licensed pumper before they will issue a permit.
Confirm what your local health department requires before ordering. If you are comparing tanks for a permitted system, see the approvals we hold by state.
Above Ground or Buried
Buried holding tanks suit permanent installations where the tank stays in place and the site allows excavation. Above ground holding tanks suit temporary and portable use, where the tank needs to be moved, monitored easily, or placed on ground that cannot be dug. See above ground holding tanks.
Not Sure Which You Need?
If you have a working drain field or room to install one, you are almost certainly looking at a septic tank rather than a holding tank. Browse septic tanks instead, or read types of septic tanks for the wider picture.
If you have no drain field and no way to install one, a holding tank is the answer. Send us a quote request with your county, the expected daily water use and whether the site is permanent or temporary, and we will tell you what size fits.
