Above Ground Septic Tanks and iterating on impermanent human sanitation
Here's a conversation I had with Gemini followed by some excerpts from the tank Depot website.
Ah, let's step completely back from the building framing and tackle your humanure puzzle directly. You are proposing an above-ground, non-septic assembly line: a toilet with a 90° outlet pointing straight out the back, feeding into a macerating pump, which pushes the slurry up to an above-ground septic/holding tank, which then feeds into a compost setup or incinerator. Is such a thing mechanically possible? Yes, but with major caveats and serious mechanical failure points that you need to weigh. Here is the breakdown of how that specific assembly line works, where it will break, and why off-grid purists usually avoid it. The 4-Stage Assembly Line Breakdown
- The Toilet & 90° Outflow
- How it works: Instead of a traditional gravity toilet sitting over a hole or a floor flange (wax ring), you use a rear-discharge toilet (often called a "back-outlet" or "wall-outlet" toilet, common in commercial settings or RVs/boats). It features a horizontal 90° waste outlet right out the back.
- The Catch: Standard household toilets rely on a massive column of water weight dropping straight down to clear the trap. Rear-discharge toilets require enough initial water force to push horizontally out of the bowl before it hits the pump.
- The Macerating Pump (The Heartbreak Engine)
- How it works: Brands like Saniflo make systems where a macerating unit grinds up solids, toilet paper, and fluids into a liquid slurry and uses internal pressure to pump it vertically or horizontally through small-diameter pipes (usually 3/4-inch or 1-inch PEX/PVC).
- The Catch (Why this is risky):
- Power Dependency: Macerating pumps require standard 120V household electricity. If your off-grid setup loses power, your toilet instantly becomes unusable.
- The "Forbidden Items" Rule: Macerating blades are notoriously fragile. If anyone flushes a wet wipe, dental floss, hair, cotton swabs, or—critically for a household with multiple daughters—sanitary products, the blades will jam, wrap, or burn out the motor. Fixing a jammed macerating pump is one of the most unpleasant maintenance tasks on earth.
- The Above-Ground Septic/Holding Tank
- How it works: The pump pushes the slurry through a pressurized line into a sealed, heavy-duty polyethylene tank sitting entirely above ground.
- The Catch:
- The Sludge Factor: Without native ground bacteria, a standard septic tank won't "digest" waste effectively without added enzymes, and it will quickly turn into a stagnant, anaerobic holding tank of liquid blackwater.
- Freezing: Since it's entirely above ground, you have to worry about winter freezing in South Carolina (though mild, a hard freeze can crack a tank or split lines if not insulated).
- Odor and Venting: You will need a dedicated carbon-filtered vent stack; otherwise, solar heating on an above-ground plastic tank will build up intense pressure and horrific sulfur odors.
- The Final Destination: Compost or Incinerator
- How it works: Moving liquid slurry from a pressurized holding tank into a compost system or incinerator is where the engineering gets tricky.
- To Compost: Raw blackwater slurry is too wet and nitrogen-heavy to dump directly onto standard compost without massive amounts of dry carbon (sawdust, woodchips) to absorb the liquid. Pumping wet blackwater into a bin creates a anaerobic sludge swamp rather than aerobic compost.
- To Incineror: Incinerators (like Cinderella or similar brands) require dry waste or specialized single-use combustible liners. They cannot process gallons of pumped liquid slurry; they would short out or fail to burn effectively. Incinerators are designed to burn dry waste at the point of use, not handle a wet, pumped holding tank output. Alternative Above-Ground Reality Checks If your primary goals are zero digging, above-ground only, and no traditional septic, the macerating pump route introduces heavy mechanical complexity, electricity dependency, and high maintenance. If you want to keep it simple and bulletproof (true to the low-tech, resource-resilient spirit of a tiny village setup), most off-grid builders skip the pump-and-tank assembly line entirely and opt for:
- Direct-Drop Bucket/Sawdust Systems: (Like the Acorn Land Labs style) where gravity drops solids directly into a 5-gallon container with dry carbon, bypassing pumps and electricity.
- Urine-Diverting Dry Toilets (UDDTs): Which separate liquids from solids at the bowl, eliminating the wet slurry problem completely and making composting clean and odorless.
Excerpts from the tank Depot website
Premium, Practical, & Portable Waste Management Solutions When underground installation isn’t possible, aboveground septic tanks—also known as waste holding tanks—provide a reliable and flexible alternative. These tanks are perfect for temporary or permanent wastewater storage in areas with high water tables, rocky terrain, or limited space. Lightweight yet durable, aboveground tanks are easy to transport and install, making them ideal for construction sites, seasonal properties, and remote locations. Their low profile build makes them ideal for many situations. They come with a lid and most of them already have molded-in fittings and multiple flat spots for additional plumbing options. At Tank Depot, we offer aboveground tanks from trusted manufacturers like Norwesco, with capacities ranging from 200 to 500 gallons. Built from corrosion-resistant polyethylene, these tanks are designed to withstand harsh environments while ensuring safe and sanitary wastewater storage.