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Can You Convert a Holding Tank to a Septic Tank?

Can You Convert a Holding Tank to a Septic Tank?


Although many people use the terms ‘holding tank’ and ‘septic tank’ interchangeably, they are two distinct sanitation systems. Both types of tanks collect wastewater from the house, but each handles the effluent differently. 

While inherently different, it is possible to repurpose one into the other. Do you have a holding tank that you’d like to convert it to a septic tank? Read on for more information about whether a conversion is possible and your best options for when it’s not.

What is a Holding Tank?

When it comes to sewage disposal, a holding tank is an important component. There are many types of holding tanks, but they all serve the same basic purpose – to hold sewage until it can be properly treated. The sewage may come from homes, businesses or industrial sites. Holding tanks are typically made of concrete, plastic or fiberglass, and  are often buried underground to prevent odors and pests from accessing the sewage.

What is a Septic Tank?

While a holding tank simply holds sewage, a  septic tank is a sewage treatment system. It is typically used in rural areas where there is no connection to a central sewage system. A septic tank can consist of two or more chambers. Sewage from the home flows into the tank where solids settle to the bottom and scum floats to the top.

Finally, the sewage flows out of the septic tank and into a leach field for final treatment. Septic tanks are typically emptied every three to five years, depending on the size of the tank and the amount of sewage produced by the household.

The Difference Between a Septic Tank and Holding Tank

There are some major differences between holding tanks and septic tanks, including their overall purpose, design and installation costs.

Overall Purpose 

The main difference between septic tanks and holding tanks is that septic tanks are designed to treat wastewater before it is discharged into the environment. Holding tanks simply store sewage until it can be disposed.


Holding tanks typically have only one lid and a single compartment. They also only have a single inlet that permits waste from the home or business to enter the tank. A septic tank is part of a system and can contain multiple compartments, multiple lids, internal baffles that direct the different parts of household waste to different areas of the tank and an outlet called a drain field where liquids are returned to the soil.

Installation Costs

A holding tank is a temporary solution for holding wastewater and costs $500 to $4,000, compared to $4,500 to $9,600 for septic systems. As the name suggests, a holding tank holds wastewater, but doesn’t have a system to filter the waste. Once a holding tank reaches capacity, it must be emptied.

Scheduled Pumping/Emptying

Holding tanks must be emptied regularly — sometimes weekly — by a truck that pumps the waste out of the tank. Septic systems are usually scheduled to be pumped every three to five years.

Maintenance Costs

Although installation costs can be high, maintenance for a holding tank is generally affordable. Once a holding tank is installed, sewage treatment professionals regularly pump out the effluent and clean the tank. Cleaning costs for septic systems usually range from $400 to $1,000, and this type of maintenance needs to be done every 3-5 years. The fee includes any tools and equipment the plumber or specialist may need.


Most states will require permitting for either holding tanks or septic systems, and the fees will vary state to state.

Will a Holding Tank Convert Into a Septic Tank?

The basic answer is no — the two tanks are completely different in their design and operation. A holding tank is a single compartment tank with no internal baffles and no outlet leading to a drain field. A septic tank is designed to operate as part of a septic system, which is in essence a mini-sewage treatment plant on your property.

A holding tank will not treat sewage at all and must be pumped out while a septic system slowly reduces household sewage to scum and sludge while draining away the liquid. If you are trying to get away from the constant need to pump your holding tank, replacing it with a new septic system is your best alternative.

Tank Depot Septic Tanks for an Alternative Solution

Can You Convert a Holding Tank to a Septic Tank?

If you have a holding tank and want to convert it into a septic system, the best solution is to replace the holding tank with a septic tank from Tank Depot. Our septic tanks are available in both single and double compartment models and range in capacity from 750 to 1,500 gallons.

Our replacement septic tanks are easily transportable and require little manpower to install, so you can do it on your time. All of our NORWESCO septic tanks that hold 750 gallons or more come with pre-assembled inlet and outlet pipes made from PVC, making the installation process a breeze. We also carry holding tanks that will work for boats, RVs, and construction site applications.

For more information on our septic and holding tank solutions, contact us today!

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