Why I love my DIY dunny

Monday – I kid you not – was World Toilet Day. It caught my eye, enamoured as I am of my country move’s second emerging miracle; the composting dunny. Waterless, silent, odourless, flyless, complete with skylight, opening casement and separate solar panel, it sits enthroned within its own long-legged cedar shed. Its simplicity and delight persuade me daily that for the planet’s sake, and the species’, the composting dunny should be ubiquitous.

Elizabeth Farrelly's toilet is enthroned within its own long-legged cedar shed.
Elizabeth Farrelly’s toilet is enthroned within its own long-legged cedar shed.CREDIT:ELIZABETH FARRELLY

World Toilet Day is serious, a UN initiative to bring safe toilets to the 4.5 billion people who live without one by 2030. Part of this push was the first Reinvented Toilet Expo, hosted by the Bill and Melinda Gates Foundation in Beijing earlier this month, to showcase the results of a five-year research program focused on rethinking sanitation.

I get it. I’m no clean freak, and am fully on board with the hygiene hypothesis (which holds that excessive cleanliness damages our immune systems). But I’ve been to places where “open defecation” is accepted and I have to say, they turn my stomach in a way that is primal.

There’s good evolutionary reason for this, of course. We know which way sickness lies. Each year some 250 million kids die from sanitation-related illness, including malnutrition. Yet it seems improbable that half the world’s population can be fully sewered-up any time soon. And honestly, even if they could, that many more water-closets would be environmentally disastrous.

This may seem harsh, but the era of the wc is over. There’s the water – which, even at five litres a flush (as in most modern loos), should be used for drinking, washing or crops. Then there’s what that water does – sluicing our shite into the hapless oceans where, even treated, it causes eutrophication, algal growth, light-loss and oxygen depletion.

It looks like a classic humans-versus-the-planet conundrum. But maybe not. If we could save the water and use the nutrients locally on land for food production, we’d save vast infrastructure and reticulation costs as well. How is this not a quadruple win?

The tiny country property where I play with these things is, to me, less hobby farm than model farm – a chance to test in the real ideas that are otherwise just ideas. Regenerative grazing, off-grid living, landscape creation – truly, it’s an experiment. And so far, one of its standout successes is the dunny.

I ordered it online and, two weeks later, collected from the local rural supplies outfit a large box of bits and connectors plus two big black buckets. All very DIY, but the instructions were good and the process simple. The only help I really needed was with the solar fan.

The fan is critical because, astonishingly, the whole process works on air. The pedestal part looks completely normal – except it’s a few steps above ground and there’s no ugly cistern. Everything collects in the underfloor bucket, with a hose taking “excess fluid” into a soakage drain. After peeing you just close the lid, but after each “solid deposit” you toss in a handful of sweet-smelling wood shavings and a couple of squirts of enzyme solution.

What’s fascinating is there’s no smell. Like, none. Embarking on this I dreaded that long-drop aroma, still so vivid from childhood camping, and the inevitable blowfly buzz. But there’s none of that – thanks to the fan (and the sun god).

 Waterless, silent, odourless, flyless, why aren't composting toilets ubiquitous?
Waterless, silent, odourless, flyless, why aren’t composting toilets ubiquitous?CREDIT:ELIZABETH FARRELLY

The fan sits entirely within the diameter of the vent-pipe and is powered 24/7 by its own solar panel and battery. It works two jobs – removing odours and, more importantly, preventing them by making sure decomposition is aerobic. (Here the composting process differs from the much stinkier, anaerobic septic tank.) The fan’s tiny comforting whirr, as it sends in an astounding 420 litres of air a minute, tells you all is good here, all is clean.

That’s the principle. But of course it’s always surprising when things go according to promise, and especially charming when they’re this low-tech. When the bucket is full, you replace it with the other and set it in the sun for six months while it cooks the pathogens out of itself. This process is thermophilic – happiest above 55 degrees C – which is why the buckets are black. The blurb says a single day is enough to kill said pathogens, so six months should be plenty. What remains is a usable humus – which you could spread as fertiliser but are required, here, to bury (at least, though, it’s still enriching soil instead of destroying oceans).

Admittedly, since my dunny has only been operating a few weeks, that second, cooking part remains for me theoretical. But it’s very simple, replicable stuff. Cheap, even. To the basic system that farmers have used for eons, modernity has brought two critical features: black plastic to absorb solar heat, and photovoltaics to supply the air to keep billions of bucket-dwelling aerobes happy and hard at work.

Since in both these the sun is paramount, it seems serendipitous that the poor countries, with the most intractable sanitation issues, tend to have most sunlight. The trick will be to use the sun’s energy to kill pathogens (rather than sweeping them to the sea), save water and feed soil.

The dunnies in the Gates Foundation Expo variously involved nano-membranes, electrolysis, pyrolysis, combustion and smouldering. They ranged in capacity from 10 to 1000 users per day, and from 0.02 to 0.1 cents each use. Some offered Wi-Fi, music and menstrual pad destruction. One, capturing methane for cooking, was net-energy positive.

A model of a self-contained toilet at the Reinvented Toilet Expo.
A model of a self-contained toilet at the Reinvented Toilet Expo.CREDIT:AP

But it makes me wonder. Do we really need to reinvent the technology, or is it already here? If off-grid, waterless onsite processing to a safe usable compost is the goal, you can do a helluva lot with a couple of buckets, some sawdust and a solar panel.

Now, if you’ll excuse me, I must visit my cedar-scented shed – with no sound to drown the frog chorus, no smell to mask the exhalation of the cooling earth and no reason to shut out a high gibbous moon silvering black hills.

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