Holding Tank vs Septic Tank: Key Differences

Do you hesitate to choose a cheaper holding tank or a septic tank that can treat wastewater due to the issue of storing wastewater? 

Although these systems may seem similar because they both store household wastewater. If you are still struggling with which product to choose, this guide explains the key differences between holding tanks and septic tanks.

Structure Differences

The internal structure of these two systems is very different. If you want to have a quick overview, refer to Table 1.

Table 1

The Difference Between Holding Tanks and Septic Tanks

Holding Tanks

A holding tank is a movable container designed to store wastewater temporarily. You will often see holding tanks used in trailers, mobile offices, temporary housing, and campers. Most holding tanks are made of plastic or fiberglass. 

Structurally, a holding tank includes: an inlet pipe and an outlet for storing and pumping wastewater. Some holding tanks have one lid for inspection and maintenance. It is different from septic systems. It doesn’t discharge wastewater into the ground. Every wastewater stays in the tank until it is pumped out.

Septic Tanks

A septic tank is a wastewater treatment system with a larger volume and a larger area. Instead of only storing waste, it separates and treats wastewater.

Most septic tanks are made from:

• Fiberglass 
• PVC
• Plastic

You’ll typically find in the septic tanks:

Inlet Baffle

The wastewater enters the inlet baffle. It is guided to the middle layer of the septic tank. It helps the scum and solids to separate into layers.

Partition wall

A partition wall is used to separate compartments.

Most septic tanks have two chambers separated by a partition wall. 

• The first chamber collects solids.
• The second allows partially treated water to flow through. 

There is an opening in the partition wall that facilitates liquid flow from the first compartment to the next, creating a layered effect.

Export baffle

It helps the flow of liquid from the middle layer of the holding tanks. These prevent the overflow of floating slag and solids from leaving the tank and entering the drain field. 

Outlet filter

It is located on the outlet baffle, used to collect small granules in wastewater.

Working Principle Differences

Holding tanks and septic tanks have different ways of treating wastewater. You can choose a suitable container according to your needs. You refer to the working principles of holding tanks below:

How Does a Holding Tank Work?

A holding tank stores wastewater temporarily until it is pumped out.

Here’s the process of working:

1. Wastewater generated at home flows into the holding tank through the inlet.
2. When your holding tank becomes full, you contact a professional company to pump the wastewater.

Important:

The holding tank doesn’t have any way to treat wastewater. It only stores wastewater.

How Does a Septic Tank Work?

A septic tank uses a natural biological way to treat wastewater.

The wastewater will be divided into three parts in the septic tank:

• Scum (floating at the top)
• Sludge (sinking to the bottom)
• Some liquids (through the drainage field)

Scum and solids are decomposed by anaerobic bacteria and enzymes, producing methane, carbon dioxide, and hydrogen sulfide. 

The treated water then returns to the soil through the drainage field.

Focus on:

Materials like plastic or metal will remain in the tank and must be removed during pumping.

Installation Costs Differences

The cost of installing either system depends on several factors:

• The price of the tank 
• Design way
• Permit requirement
• Materials selection
• Labor price

However, if you are installing a septic tank, you should consider the cost of installing the drainage system and the cost of soil testing.

You can refer to the following example:

Assuming your house has four bedrooms located in flat terrain with convenient transportation. You can refer to Table 2 for the installation costs of holding tanks and septic tanks.

Table2:

Installation Costs of Holding Tank and Septic Tank

Pumping Frequency Differences

Holding tanks need to be emptied more frequently than septic tanks. Here’s how often each system typically needs pumping.

Holding Tanks

Most holding tanks must be pumped every 1-4 weeks, depending on usage and tank size.

Septic Tanks

Septic tanks usually require pumping every 3-5 years.

You should pump sooner if:

• Your household uses a lot of water
•  The sludge water exceeds two-thirds of the total water level
• You use a garbage disposal machine to handle food waste

Maintenance Costs Differences

Normally, whether it’s a holding tank or a septic tank, the cost per gallon of pumping is the same. You can refer to Table 3 below:

Table 3:

Long-term Maintenance Costs of Holding Tank and Septic Tank

 Although holding tanks are cheaper to install, they usually cost more over time. That’s because frequent pumping can add up.

Example:

Holding Tank

A 2000 gallons holding tank

Pumping cost: $0.28 per gallon

Each pump costs: $560

If pumped once per month, annual cost: $6720 

Septic Tank

A 1250 gallons septic tank 

Pumping cost: $0.30 per gallon 

Each pump costs: $375

If pumped every three years, average annual cost: $125 

Best for：

• Holding tanks = lower upfront cost
• Septic systems = lower long-term cost

Permit Requirements Differences

Local regulations often determine which system you can install. 

If you live in the United States, the EPA (Environmental Protection Agency) has relevant legal requirements for the installation of holding tanks and septic tanks.  It lets you obtain a permit to install a holding tank, which is more complex and expensive than obtaining a permit to install a septic tank.

Holding Tanks

Officials in the United States regulate holding tank systems strictly because they require regular pumping.

You need to:

• Submit a security deposit to the relevant authorities in the jurisdiction
• Provide proof of regular pumping.
• Submit maintenance records

If you do not regularly pump the holding tank, the deposit may be used to pay for the cost of pumping.

Septic Tanks

The installation permit for septic tanks is relatively simple and can be obtained in just a few days. 

You need to:

• Contact professional personnel to evaluate the site, including soil permeability testing.
• Submit engineering design approval to the relevant website. 

After the information is approved, installation can begin.

Applications Differences

Holding tanks and septic tanks are widely used in various fields, but their applicable places are different. You need to choose according to your needs. The following is an introduction to the application of holding tanks and septic tanks.

Holding Tank

• Maritime vessels 
• Remote cabins
• Seasonal cabins
• Construction sites
• Temporary facilities
• Outside activities

Best for:

• Space is limited
• Your property has poor soil drainage
• Temporary wastewater management
• Local regulations restrict septic systems

Septic Tank

• Long-term residential
• Commercial buildings
• Hospitals
• Schools
• Rural properties

Best for:

• Long-term wastewater treatment
• Enough outdoor space
• Soil drainage conditions are suitable

Advantages Differences

Holding tanks

Warn timely: Many present tanks include level sensors and alarms to notify you when the tank is full.

Use widely: If you are in an area where a septic tank is not allowed to be used due to limitations of building standards, you can choose a holding tank.

Long service life: If maintained and pumped in time, the holding tank can be used for more than ten years.

Flexible Use: It can be used temporarily, seasonally, or remotely when you can’t pour the wastewater.

Easy installation: Holding tanks are easier to install than septic systems because they do not require the installation of a drain field.

Environmental protection: It can prevent water pollution by controlling wastewater.

Good adaptability: It has various sizes for use in the home, business, and industry.

Compliant with regulations: It is a legal solution to deal with wastewater.

Septic Tanks

Low pumping frequency and costs: You only need to pump every three to five years. You cost less money every year.

Biological treatment of wastewater: Septic tanks can handle wastewater through bacteria and enzymes.

Handle more wastewater: Some sewage from the septic tank will be returned to the soil through the drainage field. It enables them to store and treat more wastewater.

Long service life: If maintained and pumped properly, the service life of septic tanks can reach 40 years

Disadvantages Differences

Holding tanks

High maintenance costs: Pumping frequently and handling the holding tank can produce high costs. You need to pay attention to preparing permits and inspections in some states before installation, which may have additional fees.

Limited capacity: The holding tank will be filled up within a certain period of time and requires careful monitoring and arrangement for emptying.

Without the treatment function: Wastewater is not treated by any method before being pumped.

Potential overflow: Without regular maintenance, a full tank can overflow and create environmental problems.

Maintenance requirements: It needs regular inspection and cleaning to prevent the spread of odor issues, corrosion, and mechanical failure.

Septic Tanks

Regularly maintained: You need to pay attention to leakage, blocking, or overflow from the drainage field. For example, when a flood impacts the septic tank system to move or float, please contact a professional as soon as possible to handle it.

High installation costs: The cost of installing septic tanks is high. If you meet worse soil drainage and need to replace the septic tank system, it will also have high costs.

Without warning: There is no alarm in the septic tank, so you need to check it regularly to prevent wastewater from overflowing.

Strict soil and space requirements: Septic tanks require the installation of a drainage field, with strict requirements for the site and soil.

Conclusion

Both holding tanks and septic tanks can handle household wastewater. If you’re planning to buy a wastewater tank, choosing the right tank size and system type is critical. Our engineers can help you choose the right holding tank or septic solution. Contact us for a free consultation.

FAQ

1. Can you convert a holding tank into a septic tank?

Of course. However, local regulations may restrict this conversion. You’d better check with your local authorities before making changing.

2. When funds are limited, what should I choose between a holding tank and a septic tank？

If you are storing wastewater in the short term, you should choose a holding tank. It has fewer short-term costs. If you need to treat wastewater for a long time, you should choose a septic tank. Its long-term maintenance cost is lower.

3. Which system lasts longer, holding tanks or septic tanks？

Both systems can last 20-40 years, depending on materials, maintenance, and installation quality. Tanks made of fiberglass have a longer service life than those made of plastic.

4. Are holding tanks easier to install than septic tanks？ 

Yes. Holding tanks install more easily because they do not require the installation of a drain field.

5. What happens if my holding tank or septic tank is too small?

If your tank is small, it will fill up quickly. It happens:

• More frequent pumping 
• Potential overflow problem
• Higher pumping costs

Choosing the correct tank size is essential for long-term performance.