Septic tanks are fabricated using different materials. Concrete and plastic are two of the preferred types of septic tanks. Expectedly, each type of septic tank possesses several advantages and disadvantages, relative to the other. If you are choosing between a concrete and a plastic septic tank, know that, for the most part, the decision is simply a matter of personal preference. Concrete and plastic septic tanks will each come with their own set of characteristics, including average lifespan.

On average, septic tanks made of plastic or fiberglass last a bit longer, with an average lifespan of 30 to 40 years. Concrete septic tanks, on the other hand can last 40 years or more, making it the longest-lasting option.

It goes without saying that if you are needing to have a septic tank installed, it is recommended that you contract a septic system professional that has been known to have ample expertise and equipment. The type of tank you choose (whether plastic or concrete) is a factor in the process of successful septic tank installation, in itself. Property owners mostly prefer concrete over plastic tanks because these can last almost indefinitely, unless low quality concrete mix was used to manufacture it. And when it is not poured properly, it will likely fail in just a few years.

If you are planning to purchase and install a septic tank in the near future and are considering whether to go with concrete or plastic, you will want to read on.  It is important for you to understand the advantages and disadvantages of each type of septic tank.

Plastic Septic Tanks

There are many advantages to using a plastic septic tank over a concrete septic tank, which include, but are not limited to:

Advantages Disadvantages
Highly resistant to cracks, unlike concrete tanks. The lightweight plastic or fiberglass material it is made of renders it susceptible to structural damage.
Rust-proof May shift in the ground in wet soil conditions.
Lightweight material makes it much easier to transport for and during installation Could rise out of the ground, breaking pipes in the process.
 More cost-effective than its concrete counterpart. Not approved in all states.
Water-tight and corrosion-proof. Tendency to have lower effluent levels, which may be discovered after a tank is opened for pumping. This is due to dislodged tank plugs.

Plastic Septic Tank Pros. Plastic tanks are ideally made from sturdy and high-quality polyethylene, making it a much more lightweight solution. This lightweight mass translates to more affordable installation as it can be completed without the need for heavy machinery or equipment. In addition, plastic septic tanks are easier to transport and thus can be installed just about anywhere. This is an advantage if your property lies in a more remote area. Plastic septic tanks are the perfect choice for places like vacation houses and island-based properties. Plastic tanks are more resistant to the cracking, rusting, or corrosion — issues that plague concrete septic tanks down the line. A septic tank made of plastic may be installed as deep as three feet underground, which helps to protect it from the external elements and hazards.

Plastic Septic Tank Cons. Even though plastic septic tanks are cheaper and quite reliable, they do come with certain disadvantages. Because of the lightweight material they are made of, it is possible that a plastic tank could “float” in areas where the water table is higher, especially if made with the newer kind of plastic infiltrating the market today. Wet soil conditions may cause them to rise up and shift, or even tilt.  This can result to structural and leakage issues.  Also, even though polyethylene is tested and durable enough, plastic septic tanks, in general, will not be able to withstand extreme conditions as well as a concrete tank could.

Concrete Septic Tanks

There are several advantages to using a concrete septic tank over a plastic septic tank, which include, but are not limited to:

Advantages Disadvantages
Have higher effluent levels than plastic septic tanks. Susceptible to leaks and seepage through concrete cracks.
Heavy material prevents it from “floating”, unlike with plastic tanks. Vulnerable to cracks under extreme conditions.
May be long-lasting and extremely durable, depending on care and usage. Heavy weight makes it difficult to install.
Concrete tanks are approved for use in all states. More expensive to purchase and install.
Water-tight and corrosion-proof. Requires more frequent regular, periodic inspection and maintenance.

Concrete Septic Tank Pros. For several years now, concrete has been the standard building material for septic tanks, and for good reason. First of all, concrete is long-lasting. With adequate maintenance and care, a concrete tank can last for many decades. Not only are they durable, concrete septic tanks are also resilient. Septic tanks made of concrete will hold up to the rigors of heavy equipment or machinery during its installation. Should you embark on structural or property renovations down the line, you will not have to worry about accidentally gouging a hole on any part of your concrete septic tank. Finally, because concrete is a heavy material, once that tank is settled in place, you will need not fear that your tank (or its contents) will shift within the ground.

Concrete Septic Tank Cons. Septic tanks made of concrete may be relatively sturdier and solid and they may last several decades, but that doesn’t mean they will last forever. As they age, concrete septic tanks become prone to cracking and corrosion. This degradation allows toxic wastes to leak out and contaminate its surroundings. Problems can also increase exponentially when low quality concrete mix was used and/or built with steel support struts. The latter are prone to rusting, causing a slew of other issues. Concrete tanks, because they are much heavier, are much more expensive and complicated to install, requiring more skill and specialized equipment. Additionally, a concrete tank’s weight makes it more complicated and expensive to repair, should issues present themselves anytime throughout a concrete septic tank’s life. And while on the subject of lifespan, once a concrete tank hits its mortality, the heavy weight translates to the same complicated and expensive extraction.

Concrete vs. Plastic: A Closer Comparison

Being the most common materials of construction of septic tanks, concrete and plastic are the two leading tank types that many property owners compare when deciding what type of septic tank to install. While there may be many differences between the two materials, below are the ones that are most likely to be of concern to many and you should consider first:

Cost. Cost will always be a consideration in all aspects of property maintenance, including plumbing issues, so it makes sense that it is one of the first things that most property owners want to understand when comparing septic tank material. Concrete tanks tend to be relatively more expensive than its plastic counterparts. Based on statistical records, home and business owners spend anywhere between $2,500 and $7,000 just for the tank unit alone. Meanwhile, plastic septic tanks, on average, go below these average prices.

Capacity. Septic tank capacity refers to the volume of effluent it can hold. When planning on buying your septic tank for your property, you need to consider capacity. Lower-capacity tanks will, naturally, have the tendency to get filled with sludge (accumulated solid waste that settles at the bottom of the tank) more rapidly, meaning it will require more frequent pumping.  The opposite is true for a bigger septic tank. Besides that, a small septic tank has a lower effluent retention time. Effluent retention time is the length of time the effluent is held in the tank before it is pushed into the drainfield. A significantly short effluent retention time means that the effluent in your tank will be pushed into the drainfield prematurely — before liquid and solid wastes have been sufficiently separated, resulting to what is ideally a clear liquid substance, This kind of prematurely treated effluent will pollute and damages your drainfield.

Durability and Potential for Damage. The other thing you need to consider is how sturdy (or fragile) your septic tank material is. Concrete septic tanks are more susceptible to cracking than their plastic counterparts. The likelihood of cracking is especially high if the actual concrete mix used in manufacturing the tank is not of good quality or when it wasn’t mixed in the proper ratio. Effluent can leak out of the septic tank through the cracks and contaminate your surrounding soil, plants, or even water. Likewise, seepage of groundwater into the tank is also possible, resulting to overloading and eventual blockages. The problem is you may not notice the seepage in time before it escalates into more serious septic problems. Plastic septic tanks, on the other hand, won’t crack or corrode as easily as concrete, but these can be susceptible to damage if subjected to too much weight, pressure, or unfavorable soil conditions. Possible scenarios include driving vehicles or heavy machinery over where a plastic tank is buried and wet soil conditions render a plastic septic tank vulnerable to “floating”, shifting, and tilting.

Your Third Option: Steel Septic Tanks

There is a third option on the list of septic tank types: steel septic tanks. Surprisingly, however, septic tanks made of steel are the least durable and least popular option. Steel septic tanks are designed to last you about 20 to 25 years, at most. This is because steel septic tanks are susceptible to rust corrosion which could take place long before the 25-year lifespan is even reached. Similarly, the steel septic tank cover can rust through and deteriorate, exposing the property’s occupants to serious physical hazard from caving in with even just the weight of a person. If what you have or what you’re considering is a steel septic tank, remember that the steel covers that it comes with will need to be replaced periodically. The bright side is that these covers can be replaced without having to replace the whole tank. Steel septic tanks might require more frequent manual inspection and periodic maintenance. Also, as with any other septic tanks, you will need to pay closely monitor the baffles (entry and exit points) of steel septic tanks as these tend to get degraded first.

Just How Important is Septic Tank Design and Construction?

A septic tank needs to be well-designed and solidly built so that it will not easily crack or corrode, resulting to groundwater contamination. When purchasing a septic tank, it matters that you consider its design and construction of a septic tank, determine effluent levels each type of tank can hold, as well as other aspects of design such as tank inlet and outlet pipes, internal chambers and accompanying transfer pipes, vent pipes, and the design of access manholes. All these are factors in the maintenance of the tank you finally decide on.

Never underestimate the forces that a particular type of septic tank has to withstand. Consider that the slightest ground movement, especially with inadequate reinforcements on the tank’s actual placement, could be enough to inflict cracks on your septic tank. A well-built septic tank will not leak and should be able to withstand earth movements, changing soil conditions, and the like and not crack under the slightest of pressures.

Consider, too, that an operational septic tank may be holding as much as a metric ton (or 1,000 kg) of liquid for each cubic meter. For an average tank, this can be as much as 3 or 4 tons. That is a lot of weight.

Environmental pressure plus load weight are major considerations, often contradicting each other. Add to the equation your property location and other logistics and things can get more complex in no time. The main thing to remember is to find the most suitable tank based on all these factors. Professional advice from septic contractors thus comes valuable. Septic tanks should either be made from durable plastics that will allow for a little “give” with ground movement or be built with reinforced concrete and designed in such a way that, in the event of ground movement or drastic soil condition changes, your septic tank will be flexible enough to remain intact and formidable enough to keep its integrity.

One of the first things you need to determine is how big of a septic tank your type of property requires. It is essential that your septic tank is large enough to accommodate the number of occupants it will serve. There are several reasons why a septic tank can easily become full and eventually overflow. Lifestyle or usage habits directly affect the volume of water that will go into your property’s septic tank. If your property is situated in a generally hot climate region, your occupants are likely to be taking baths more frequently and/or for longer. More occupants translate to more laundry and/or significantly more kitchenware that need washing. It has also been found that the more affluent a household is, the higher the water consumption.

A septic tank should have at least two chambers. Having 3 is better, yes, but 2 is enough. The first chamber needs to be around twice the size of the second chamber. A typical household septic tank can be made up of two round tanks. Or you may just one rectangular septic tank divided into two chambers, instead of having two separate tanks. Septic tanks are designed to have a division between two sections, with the first compartment being twice the size of the second. Most of the sludge (accumulated solid waste) is held in the first tank or section, while sewage undergoes further treatment to remove residual solid waste in the second tank or section.

And so, you ask again: which material is best for septic tanks? This really depends on the quality of your soil. In case there is a high level of acidic groundwater in your soil, it can eat away at a concrete septic tank.

Obviously, both concrete and plastic septic tanks are good options when it comes to this kind of decision-making. Upon weighing all the advantages and disadvantages and everything else considered, it might seem clear why a lot of people believe that septic tanks made of plastic are the smarter choice, in the long run.  Strong, long-lasting, and much more affordable than concrete, and, should something go wrong down the line, you need not exert almost insurmountable effort or spend a hefty sum to get then removed, fixed, or replaced. When is a concrete septic tank appropriate, then? First, of course, is when concrete is mandated by zoning codes applicable to your property. Likewise, septic providers opt for concrete when value is more of a consideration over actual cost. The septic company that you hire should be able to inspect the land in your home or business property and make a professional recommendation on what tank you need to install.

Septic systems can last you anywhere from 15 to 40 years. It seems like a wide range, but that is because the average lifespan depends much on factors like how regularly it is pumped, how frequently it is inspected, and the usage habits of those who occupy the property. Having your septic system regularly serviced and maintained is the easiest way to improve its lifespan.