How to Make a Simple Composting Toilet

The following has been rated PG, Pretty Gross, by the Mainstream Potty Association of America. You’ve been forewarned.

The kids and I slept in sleeping bags in the dome for the first few nights, while Mauricio chose to stay nice and warm in the RV, thank you. From the bay window, the night sky without light pollution is simply stunning. And it turns out that the Great Horned Owl we hear at dawn and dusk is not talking to himself. In the silence of the outdoors, without the thick walls of the RV, I heard a second and then a third owl having a complete conversation across the canyon. I also loved waking early to natural light streaming in as the kids were still snuggled in and sleeping.

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But the second night, we froze our booties off, so we decided to wait until the dome is ready for us full-time. We’re looking into efficient woodburning stoves. More about that soon. But the other thing we need, besides a kitchen set-up, is a toilet situation.

We’ve been using the RV toilet which goes to a holding tank under the RV. The thought alone of a tank of poo underneath us is enough to gross me out. When the tanks are full, we open up the hoses and the black water goes into a basic underground septic tank that the previous owners had put in. We’re not sure what the capacity is, or how much was already in there, so we’re gambling that we’re not going to flood it.

There are a few problems with our current system, of which the primary can be summed up in two words: skid marks. RV toilets don’t have sitting water, but are dry. Then you have to come out of the bathroom, turn on the water pump, and step on the lever that flushes contents into the tank. As you can imagine, or maybe you prefer not to, the toilet bowl is pretty gross most of the time. Add to that the rank smell of emptying the tanks weekly (which has mostly been Mauricio—talk about Dirty Jobs) and you’ve got plenty of motivation to improve on the method.

A digression: When I was in the Peace Corps, I was the only American on an island of about 130 people. One of the requirements to host a volunteer was that they build an outhouse. Mine was the only outhouse on the whole island. I soon found out why. Within two months, the outhouse was filled with giant cockroaches. I do not exaggerate when I say there were hundreds of those 2-inch suckers in the outhouse. Soon, I too, was “going to the bathroom” the way the Marshallese do. During the day, you go to the ocean side, squat in the low reef, then use a few rocks to wipe. The tide carries it away. During the night, you go to the closer lagoon side, dig a hole in the sand, cover it, then wash in the lagoon. Believe me, it was a whole lot more sanitary than that outhouse. And washing with rocks and water was a basic bidet system that got you cleaner than toilet paper. So let’s just say I’m no stranger to considering alternative toilet options.

Because of the nasty RV toilet, and fear of smell with a composting toilets, Mauricio has been pretty insistent that we get some kind of P-trap toilet that has a water seal. However, our water tanks are about a third of the way down, so we know we’re going to have to conserve water.

We looked into several commercial composting toilets. But they’re expensive ($1000 or more) and seem complicated, with traps and incinerators and fans, and such. Also, they seem to have a lot of parts and varied surfaces, and I want something that’s easy to clean (if you’ve ever gotten under your toilet and cleaned the P-trap and floor in the back, you know how nasty all those surfaces get).

There’s this permaculture principle that says to use small and slow changes, which applies nicely here. We would try the easiest, cheapest solution to see if it works (i.e., doesn’t stink, isn’t too much upkeep) before moving on to more complicated solutions, without losing too much time or money. Soooo, we decided to try the most basic composting toilet. It’s based on the Lovable Loo and the Humanure Handbook, which is a good read that really does make you reconsider how we use drinking water to flush away our human waste. Yes, you can drink the water from your toilet tank. Just ask the CDC.

The Lovable Loo system works like this: you “go to the bathroom” in a bucket, cover it with sawdust, then dump the bucket into a dedicated compost heap, where it sits for a year and turns to compost. Supposedly, it doesn’t smell. Uh-huh. We’ll be the judge of that.

Like most of the stuff we’ve done, we hacked our own plans. The Lovable Loo is a plywood box raised on legs, but we wanted a completely closed box, so you don’t see the bucket sticking out underneath (a more aesthetically pleasing toilet, if you will). So we figured ours based on 20″ x 18″ sides and 18″ x 18″ front and back.

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We pre-drilled screw holes on scrap posts and then screwed the cube sides together onto the posts.

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Because we made the box taller than the plans to accommodate our height, we had to raise the bucket, which we did by screwing on ledges and putting in a scrap piece of plywood.

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For the top, we figured out where the toilet seat should go—close enough to the edge so you don’t scrape the back of your knees on the square box edge—then traced and cut out the hole for the bucket.

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We put hinges on the back edge, so you can open up the top for removing and emptying the bucket.

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We had to move the bumpers on the underside of the toilet seat to the outside of the seat, where they would meet the plywood, instead of sitting on the edge of the bucket.

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Then we drilled the holes for the toilet seat and screwed it on.

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We used a bucket we already had, and we got another big bucket full of free sawdust from the local lumber company.

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And voila! Our new composting toilet. I still have to apply a few coats of polyurethane left over from the dome deck. Wood is absorbent, you know, and we don’t want that. So we haven’t tested it out yet, though I had three eager and willing little volunteers. And we still have to find a good location and set up our compost dump pile. But all in all, I’m very excited about our solution. The best part about it is the straight drop into the bucket with nowhere to leave skid marks, no toilet bowl to clean. I really hope it doesn’t stink. If it does, our next step is to use a urine separating inset, which is supposed to prevent odors by separating the liquids from the solids.

I’ll report back as soon as I have, um, data.

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