Septic Tank vs. Holding Tank: What to Know About Each

If you’re thinking of building or buying a rural home or cabin, you’ll need to address how you’ll deal with household sewage. There are several options. Two of the most popular are a septic tank with an accompanying septic system, and a sewage holding tank.

Choosing which makes sense for you begins with understanding how they differ. I’ve lived with a septic system for many years and know all its ins and outs. I also know folks who have gone the holding tank route. Keep reading to learn how each approach works, and their pros and cons.

What Is a Septic Tank?

Septic tanks are large underground containers that receive and distribute household sewage and wastewater. They’re usually made of plastic, concrete or fiberglass, and range in capacity from around 1,000 to more than 4,000 gallons. They’re most often installed on rural properties where municipal waste disposal isn’t an option.

A single, large-diameter sewage pipe connects the septic tank to the house or cabin. Once the wastewater reaches the tank, it passes from one internal compartment to another, then flows out of the tank through a series of pipes into the surrounding soil. During this process, microbes break down the waste material, purifying it naturally.

Along with wastewater, solid waste and oily sludge also collect in septic tanks. This needs to be pumped out every few years by a septic contractor with a special vacuum truck.

What Is a Holding Tank?

A holding tank is exactly what it sounds like — a large tank that receives and holds household sewage and/or wastewater. Like septic tanks, they’re made of plastic, fiberglass or concrete, with a similar size and capacity range. Also like septic tanks, they connect to household sewage systems through a large diameter pipe.

But unlike septic tanks, holding tanks don’t distribute waste anywhere and offer no means of sewage purification. When they reach capacity, they need to be emptied by a septic contractor with a vacuum truck.

Holding tanks are used where septic systems aren’t practical due to location or soil type. They also can be a temporary solution for homeowners who wish to occupy a new dwelling before the septic system is installed.

Septic Tank Pros and Cons

Having lived with a septic tank for decades, I can speak with considerable knowledge of their pros and cons. When combined with a well-designed septic system, septic tanks offer a great way to dispose of household sewage. But they’re not without their downsides.

Pros

• Convenience: When combined with a well-built septic system, septic tanks provide a way to dispose of all household sewage, supporting a fully modern lifestyle without municipal waste disposal.
• Longevity: A well-designed and well-managed septic system can last for decades without any major repairs.
• Independence: As long as you have the space and proper land conditions, you can set up a septic tank and system anywhere. This allows rural cabin life to be much more comfortable, thanks to modern indoor plumbing.

Cons

• Expense: Proper septic systems are costly to install, particularly if you need truckloads of soil brought in to finish the job. It’s easy to spend $15,000 or more on a septic system installation, and it’s not a job most people can DIY.
• Maintenance: Septic tank maintenance requires pump outs with a vacuum truck every few years, costing $300 to $600 a pop.
• Failure: No septic system lasts forever. Even if you take exceptional care of yours, after a few decades it will likely need to be redone.

Holding Tank Pros and Cons

I’ve never lived with a sewage holding tank myself, but know friends who have. Here’s the condensed version of the pros and cons they shared.

Pros

• Low-cost installation: Unlike septic systems, holding tanks don’t require huge amounts of dirt to be moved and complex perforated pipe installations. For this reason, they’re much cheaper to install than septic systems. If you have the tank dropped off where you want it, you could make the sewage connection yourself.
• Simple: Holding tanks are just a pipe and a tank. Unlike septic systems, there aren’t many things that can go wrong if it’s installed properly.

Cons

• Ongoing expense: Septic tanks need to be pumped out every few years. With holding tanks, it’s more like every few weeks. At a few hundred dollars per vacuum truck visit, this expense adds up fast.
• Not allowed everywhere: Some locales have strict rules about where and how sewage holding tanks can be installed. Others don’t allow them at all, due to the environmental risk if one ever leaked or overflowed.

Can You Convert a Holding Tank Into a Septic Tank?

Technically yes, but check with local authorities to make sure it’s allowed in your area.

Assuming it is, the first step is positioning your tank and connecting it to your home’s drain pipes. Next, you’ll need to install a short stub of PVC pipe in the other end of the tank (the outlet) with a cap glued to it to prevent sewage overflow. From there, you’re good to go.

Just make sure you call for a pump out before the sewage level reaches the height of the tank outlet, just to be safe.