Like any kind of living arrangement, living in a tiny house can come with its own drawbacks, like problems with bathroom waste disposal. Most tiny homes utilize composting toilets or portable septic tanks for holding waste, but these will eventually need to be drained -- which can be a messy inconvenience. If your tiny house is more permanently settled, you should consider setting up a septic system. 

So what exactly is a tiny house septic system? A septic system is an underground treatment structure for wastewater, where a combination of nature and technology treat the waste produced by tiny homes. Although septic systems are usually seen in rural areas, setting one up can greatly improve the way you use running water and the toilets in your tiny home. 

How Drainage Works For Tiny Homes

Before discussing how plumbing and drainage works in a tiny house, it’s important to discuss the difference between greywater and black water.

Greywater is relatively clean waste water coming from the shower, sink, or washing machine of your tiny house. Although this kind of water can contain materials like soap, hair, dirt, bacteria, and grease, greywater can be reused when disposed of into the ground. Plants and trees filter the waste and use the nutrients as fertilizer, as long as all the materials are biodegradable. 

On the other hand, black water is toilet waste which includes urine and feces. This substance needs to be disposed of properly or else it heavily pollutes the dumping area.

Living in a traditional house on a fixed foundation requires plenty of effort as you’ll need to dig trenches and run pipes for plumbing and drainage. On the other hand, tiny houses require a different strategy. Since most tiny homes are designed for portability, installing expensive pipes everywhere you travel is not a practical option. 

Some tiny houses on wheels (THOW) follow the routes that recreational vehicles (RVs) take: they store their wastewater in separate tanks until they can dispose of them at a dumping station. Other THOWs opt to use either a composting toilet or an incinerator toilet to convert their black water into soil or ash. These options allow them to manage the weight limits for their homes. 

If you’re on-grid but would like to travel with your tiny house every now and then, a septic system is the best choice for drainage. An effective septic system will allow the ground to absorb waste water while holding onto solid waste in its chambers so it breaks down and decomposes first. 

Read more: Best Practices For Easy Grey Water and Black Water Maintenance In Tiny Homes

How a Tiny House Septic System Works 

While urban areas usually allow access to a sewer point, you’re more likely to encounter a septic system in more remote places. A typical septic system is made up of two parts: the septic tank and the drainfield (or soil absorption field).

A tiny house septic system has drainage pipes set up around your house, leading outside or underneath if you’re a mobile tiny home. These waste pipes converge and connect to a septic tank, which separates the floatable materials like solids, oil, or grease in the waste water. 

Floatable materials remain in the septic tank as bacteria breaks down the bodily waste, while the liquid is discharged. The liquid, called effluent, passes through a series of pipes buried in the drainfield until it is slowly released into the soil or surface water. In some cases, the soil absorption field is a pile of sand, organic matter like peat and sawdust, or constructed wetlands. These materials help remove and neutralize any pollutants in the waste. 

Setting Up Your Septic System 

Before you start installing pipes, you will need to secure a building permit. As regulations can vary per region, start by consulting a contractor so you can get clearer details. Generally, regulations require a household septic tank to have a 1000-gallon capacity. As a tiny house, you can opt to have a septic tank that can hold 750 - 900 gallons. 

Once you have your permit, it’s time to choose the material for your septic tank; concrete, plastic, fiberglass, and steel are the more common options. Here is how they stack up against each other: 

MaterialCostLifespanPros or Cons 
Concrete $600 - $100040 yearsHeavy; takes up too much space; may be more expensive to install 
Fiberglass$1400 - $160040 yearsLightweight; more affordable installation vs concrete; prevents roots from pressing into the tank 
Plastic $900 - $100040 years Lightweight; cheaper to install; ribbed design prevents roots and soil from cracking the plastic 
Steel $800 - $1000 20 yearsProne to rusting 

Depending on your location, the labor for installing a septic system can cost anywhere between $1500 - $5000. The cost increases if your tank is too heavy to move around and if there is a lot of ground that has to be cleared. 

Although this may seem like an unreasonable price to pay, it also means that your septic system will only need to be pumped out every 3 - 5 years. This is a much better alternative to the more inexpensive option of using a holding tank system but having to pump everything out by yourself weekly. 

Aside from installing the septic system itself, you may want to consider adding a vent pipe to prevent odors from entering your home. A septic tank specialist would know where best to put the vent pipe in your tiny space and ensure your toilets will flush correctly. Professionals would also be able to run the pipes directly into the tank and far away from your property. 

It’s important to keep your septic tank away from the tiny house, as it can cause the ground to soften and sink your home. You should also protect your septic tank from heavy rains, ground water, and any nearby plant roots to preserve its functionality. 

Watch this interesting video from one tiny house owner, a quick overview of the drainage system they currently have for their tiny home:

Dispose Water Waste Cleanly and Safely From Your Tiny Home

Establishing an effective plumbing and drainage system ensures that you and your surroundings remain clean and odor-free for your family’s health. Be sure to do enough research and consult with professionals before you set your septic system up. 

About Us

Manuela and Ivan from Tiny House Bloom

Hey, there! We're Ivan and Manuela from Croatia, and we're crazy about tiny houses. We don't own one (yet).

This website is a result of our passion to share all the knowledge, photos, tips and tricks that we were able to learn while studying everything possible about the tiny house movement.