Holding tanks vs. septic tanks: What’s the difference?

Premier Tech Water and Environment installer making sure that a septic tank is level before backfilling.

If you are buying a rural property with a holding tank or septic tank, you may think they do pretty much the same thing. They’re both septic systems, right?

Not exactly.

There are six major differences between holding tanks and septic tanks: they have different purposes, appearances, installation costs, pumping schedules, long-term maintenance costs, and permit requirements.

By knowing the ways in which holding tanks differ from septic tanks, you can make an informed decision before you purchase your dream property in the country.
 

Holding tanks and septic tanks have different purposes

Holding tanks and septic tanks work differently.

Both systems receive your home’s sewage, but holding tanks offer no treatment and have no outlet. They store raw wastewater until a pumper removes it.

Septic tanks provide primary treatment by allowing wastewater to separate into three layers. Scum rises to the top of the tank, solids sink to the bottom, and partially clarified liquids flow through an outlet pipe for further treatment or final dispersal.
 

Why would a house have a holding tank?

A house or cottage would use a holding tank if it had no connection to a municipal sewer and unsuitable conditions for an on-site septic system. Holding tanks may also be used during new constructions before a more permanent sewage system is installed.
 

Why do some houses have septic tanks?

Houses and cottages use septic tanks if they are not connected to a municipal sewer, and they have suitable space and soil for an on-site septic system. Recent estimates show that more than 21 million households in the United States use septic tank systems to treat their wastewater.
 

Holding tanks and septic tanks look different

It is easy to see the differences between holding tanks and septic tanks when you compare these features:

  • number of lids
  • number of compartments
  • partition walls
  • tank outlets
  • high-level alarms
     

What does a holding tank look like?

2D diagram of how a conventional holding tank looks on a residential property.

In many cases, residential holding tanks — sometimes known as tight tanks — have one lid and one compartment.

Because a holding tank’s purpose is to store wastewater, it has no partition walls and no outlet.

Inside the unit, a high-level float connects to an alarm that activates when the tank is almost full. This prevents over-filling that could result in a sewage backup that spills into your home or contaminates the environment.
 

What do septic tanks look like?

2D diagram of how a conventional septic tank and septic drain field look on a residential property.


Residential septic tanks usually have two lids and two compartments.

Unlike holding tanks, septic tanks also have internal components that allow them to partially clarify your wastewater:

  • Inlet baffle
    The inlet baffle directs incoming wastewater downward toward the mid-level of the septic tank. This keeps surface scum from clogging the inlet pipe. It also makes it easier for solids to naturally settle on the bottom of the tank.
     
  • Partition wall
    Sometimes called a baffle wall, the partition wall separates compartments inside the tank. It helps to keep scum and solids in the first compartment. It also has an opening that allows liquids to flow between compartments.
     
  • Outlet baffle
    The outlet baffle draws liquid from the mid-level of the tank and directs it to the outlet pipe. This prevents sludge and scum from leaving the tank and clogging downstream components.
     
  • Effluent filter
    The effluent filter is a device in the outlet baffle that can be removed and cleaned. It traps and retains fine particles that would otherwise clog downstream components.
     

Holding tanks and septic tanks have different installation costs

Holding tanks are cheaper to install than septic tanks.

It all comes down to their designs. Holding tanks are simple storage systems with no outlet. Unlike septic tanks, their designs do not include:

  • wastewater treatment components
  • extensive piping
  • large amounts of granular materials, such as sand and gravel
  • drain field (also known as a leach field) where effluent returns to the site’s soil
     

Holding tank installation costs

Total project costs to install a holding tank include several factors. There is the price of the tank, of course, but also designs, permits, materials, and labor.

For example, let’s assume that you have a family of four. You choose a polyethylene holding tank with a capacity of 2,000 US gal. Also assume that your property is flat and easy to access.

In this scenario, the total project cost to install the holding tank would be between $6,500 and $8,000.
 

Septic tank installation costs

Total project costs to install a septic tank also depend on many factors. The most obvious costs are the septic tank and its drain field. But you also need to plan for the expenses of soil tests, designs, permits, materials, and labor.

As an example, say that you have a four-bedroom home. You choose a polyethylene septic tank with a capacity of 1,250 US gal. Let’s also assume that your property is flat and easy to access.

In this case, the total project cost to install the septic tank and its drain field would be between $12,500 and $22,000.
 

Holding tanks and septic tanks have different pumping schedules

Holding tanks need to be pumped more frequently than septic tanks.

The reason is simple. Holding tanks retain all the sewage that flows into them. Septic tanks retain solids and scum, but they allow liquid wastewater to return to the site’s soil via a drain field.
 

How often do holding tanks need to be pumped?

Holding tanks need to be pumped often to prevent sewage backups in your home and environmental contamination. Depending on the capacity of your tank and the amount of wastewater your household generates, you can expect to need a pump-out every one to four weeks.
 

How often does a septic tank need to be pumped?

In most cases, residential septic tanks are pumped according to schedules laid out in local regulations. As a general rule, you should have your tank emptied every three to five years, or when the sludge level exceeds two-thirds of the total height of water in the tank.

Pumping may be needed more often if you use a garbage disposal for your food scraps.
 

Holding tanks and septic tanks have different long-term maintenance costs

Septic pumper using a hose to empty sludge from a residential septic tank.


The price per gallon to pump holding tanks and septic tanks is usually the same. But because holding tanks require emptying every one to four weeks, they have far higher long-term maintenance costs.

These expenses can create a heavy financial burden for some homeowners — so much so that many jurisdictions in the United States discourage or even prohibit the installation of holding tanks.
 

How much does it cost to pump a holding tank?

The cost to pump a holding tank depends on its capacity and the region where you live. A tank that holds 500 US gal costs about 40 cents per gallon, whereas a tank that holds 2,000 US gal or more costs around 28 cents per gallon.

These rates include your septic pumper’s additional fees, such as labor, travel expenses, and permits to discharge sewage at locations designed for that purpose.

Let’s say that you have a holding tank with a capacity 2,000 US gal. Assume, too, that the cost of pumping is 28 cents per gallon. The final bill for each pump-out would be $560. Even if you need service just once a month, you can expect to pay $6,720 over the course of a year.
 

What is the average cost to pump a septic tank?

The cost to pump a septic tank depends on its volume and the area where you live. On average, a tank for 500 US gal costs 40 cents per gallon, a tank for 1,000 US gal costs 32.5 cents per gallon, and a tank for 2,000 US gal or more costs 28 cents per gallon.

Your pumper may charge additional fees if your tank’s lids are buried and require excavation.

To see these rates in action, imagine a septic tank with a capacity of 1,250 US gal. Assume that the cost of pumping is 30 cents per gallon. The cost to have your septic tank emptied would be $375. If your tank requires a pump-out every three years, the overall cost works out to just $125 per year.
 

Holding tanks and septic tanks have different permit requirements

In some parts of the United States, getting a permit to install a holding tank is more complex and costlier than getting a permit for a septic tank.

The reason is that holding tanks pose a unique challenge: they threaten the environment if they are not emptied as needed, but the ongoing pumping bills are too expensive for some household budgets.

To prevent environmental contamination, some jurisdictions issue a permit for a holding tank only if you post a bond and agree to show proof of regular pump-outs. Local authorities then use the bond to pay for pumping if there is reason to believe that service has lapsed.

The permit process for septic tanks is simple by comparison. In many states, you can get a permit, often in just a few days, when you provide this information:

  • site assessment results, including soil percolation tests
  • design plans for your system
  • names of the technologies you want to install
  • details about the installer
     

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