How I made a simple outside compost toilet.

Pictured is my compost toilet
Tiny house outdoor compost toilet

In this post I will describe how I built a simple outside compost toilet that was used during the construction phase of the tiny house project.

I chose a compost toilet for simplicity, to save water and because my tiny house is not connected to any sewage network. You can read more about the ultra simple ‘biolitter’ toilet here.

The image to the left shows my compost toilet setup. Building it was the first job I had to do!

As you can see, it consists of a box made from OSB. The top face of the box is removable and a large galvanised steel bucket is placed inside. I had to fix more OSB inside the box to raise height of the bucket to just under the top face. The last job was to cut a hole in the top and screw on a toilet seat.

Next to the toilet was placed a plastic bucket containing the compost ‘litter’. This has a lid to keep the litter dry and keep out creepy crawlies.

In order to keep the toilet stable on the uneven ground, I placed it on another piece of OSB.

Toilet Enclosure

The toilet was placed in a pop-up shower cubicle with a zip-up door.

Pictured is a decathlon pop up shower cubicle
Pop up shower cubicle for compost toilet

I got mine from Decathlon ( a French outdoor products retailer).

The cubicle is quite handy in that it goes up very quickly and packs down into a small space. There is also a mesh pocket inside for putting shampoo, hand sanitizer etc.

I actually bought two cubicles and used the other one for the solar shower.

Each cubicle cost £49.99 which is ok. I considered building a toilet and shower enclosure from wood, but that would have cost more, taken longer and would eventually need to be dismantled and disposed of. The cubicles have been great in that they can be quickly installed and removed each time I visit the tiny house.

As the cubicle is open at the top, I used un umbrella to cover up the hole when the weather was bad. You could just as easily tie on some plastic sheet or material from an old tent.

Compost toilet litter

For the compost toilet litter, I initially bought a bale of wood shavings from a local agricultural co-op (these are very handy shops in rural France and you can buy all sorts of items: hardware, work clothing, garden items and even local food and drink).

Anyway, the wood shavings are said to be better than sawdust as there are more airspaces and so the compost is better aerated.

After each visit to the toilet we added a handful of litter and the bucket was emptied every day or two. After emptying I gave the bucket a good rinse with the garden hose, added a layer of litter and it was ready to be used again.

The wood shavings worked ok and lasted for most of the first summer (about 6 weeks). Later on I switched to using hemp as I had a large quantity left over from the tiny house build.

It turns out that hemp is well suited for use in compost toilets. I didn’t know it at the time, but hemp is also sold for use as animal bedding. One supplier claims that is is more absorbent than wood shavings or straw and is also good at reducing odours. I also learned recently that a Dutch company make public urinals that use hemp, the end result being an organic fertilizer. Apparently hemp composts quite easily.

So, hemp seems like the ideal stuff for my compost toilet and luckily I have loads of it lying around. So that’s what I will be using for quite a while!

The Compost Heap

My first compost heap was very quick, cheap and simple. I made it from reed garden screening that I screwed to 4 wooden posts hammered into the ground.

Pictured is a sketch of a compost heap
Quick and simple compost heap

The base was about 0.8m square and the height about about 1.2m.

Besides the toilet waste, I also used added food scraps, waste paper and some cardboard.

Each time I added toilet waste onto the heap, I also added a bucket of dry hemp on top.

By the end of the summer, the heap was nearly full.

Some months later I noticed that the pile of compost had shrunk a little and when I turned the top layers over, there was steam coming from the middle. So its seems that the decomposition process was working.

Bad Smells?

Yes and no.

As the toilet cubicle was open at the top and the toilet itself had a lid, it wasn’t smelly in the toilet itself. At times it was used by me, my 2 children and my 2 step-children and nobody complained!

The compost heap did produce some odours though. Absorbent as the litter is, there always seems to be some urine at the bottom of the bucket. When emptying the bucket onto the compost heap, this liquid is then at the top. Although I did add a layer of dry hemp, there still tended to be a urine odour coming from the heap. It didn’t help that the compost heap was close to the house. Putting more dry hemp on the heap reduced the smell but also filled the heap up quickly.

In future I will locate the compost heap further from the house (but not too close to the neighbours!) and will make it a bit bigger so that I can add more dry hemp.

Next steps – An Inside Toilet

The next stage of the building process is to complete the shower room inside the tiny house. Apart from the shower, it will also have a compost toilet and a wash hand basin.

My plan was to build another compost toilet, albeit a more ‘attractive’ version, something like the one shown below.

Pictured is a compost toiler
Portable Compost Toilet

However, I came across a ready made plastic camping toilet which looks worth a try.

At around £30, it’s not much more expensive than the price of a new toilet seat. It has the advantage of being less bulky than a home made ‘square box’. This could be a real bonus as the shower room is very small (little more than a cupboard). The shape looks like it would give more space for the user’s feet while sitting. It’s also a comfortable height (44.5cm). The 22 litre capacity should mean that I don’t have to empty it quite as often too.

Pictured is a plastic camping toilet
BranQ camping toilet

So I went ahead and ordered one and will try it this summer. I also ordered some compostable plastic liners for the toilet. These will help keep the toilet clean and may also reduce odours from the compost heap if it gives the hemp a bit more ‘absorbing time’ before the bag decomposes. The risk is that they don’t actually decompose very well and/or they impede the aerobic process. I guess I’ll find out soon enough!

Why I chose a biolitter compost toilet

In this post I’ll explain why I chose to use a compost toilet and, more specifically, a simple biolitter type.

Water Savings

The waste of an expensive commodity like mains water was something I was keen to avoid. After washing, toilets are the biggest consumer of domestic water. A report by the Energy Saving Trust in 2013 found that 22% of water consumed in UK homes was used to flush toilets. Furthermore, it just seems crazy to use high quality drinking water to flush a toilet.

An alternative is to use a compost toilet. Having previously read about simple compost toilets (and seen them in use at an eco-centre) I decided early in the design process that I would use one for my tiny house.

Free Garden Compost

A further bonus is the recycling of human waste and kitchen scraps to make a high quality compost that can be used in the garden. To be fair, it’s not completely free as you normally have to buy the ‘biolitter’ (sawdust, wood shavings, etc) to which the waste is added. However, I had lots of hemp left over from the build which was ideal for this purpose.

The Biolitter Toilet

The compost toilet system I chose was popularized (in French speaking Europe at least) by Professor Joseph Országh of the Université de Mons-Hainaut in Belgium. He called his system the “toilette à litière biomaîtrisée” or TLB . This can be literally translated as “biocontrolled litter toilet” or “biolitter toilet” (BLT). US readers may be familiar with a similar system called Humanure proposed by the American Joseph Jenkins.

For the benefit of this website’s English speaking readers, I’ll stick with the term Biolitter toilet (or just compost toilet) and avoid the acronym BLT, for obvious reasons!

Whatever the name, the principle is the same. In place of a normal toilet is a bucket with a volume of 20-40 litres. Around the bucket is built some kind of containing ‘box’ with removable top. This top has a hole around which is fixed a toilet seat and lid.

After each visit to the toilet, the waste (solid and liquid) is covered by a layer of ‘litter’ which is typically wood chips, wood shavings or sawdust. The cellulose in the litter biologically inhibits the enzymatic reactions in the excreta that are responsible for odours. Nevertheless, the bucket should be emptied at least once per week.

The bucket’s contents are then composted for at least two years (along with kitchen food scraps etc) after which the compost is safe to use in the garden.

I briefly considered other types of compost toilet but they seemed to be more expensive and complicated. I didn’t see the point of buying a commercially made item when I could make a very simple, proven and low cost system myself.

The Biolitter toilet in practice

I used a home made outside biolitter toilet for two summers while the tiny house was being built. It was very simple and convenient. You can read about it here.

In the summer of 2021 I started using a biolitter toilet inside the tiny house. This time I used a plastic bucket type toilet with an integrated seat and lid and it was placed in the shower room. This toilet is very compact which was ideal for the small space available. In practice it has worked well. Even my teenage daughter has given it the thumbs up for it’s practicality and surprising lack of odour! She even says that she will use a compost toilet in her house when she is older.