Build Your Own Composting Toilet

diy separating composting toilet

After many years using a chemical cassette toilet we've decided to move over to a home made composting toilet, mainly due to the fact that they are incredibly low maintenance and you can empty them pretty much anywhere!

But don't they smell?!

Composting toilets can smell. However, so do normal toilets, and chemical toilets, and pretty much any toilet. The way to minimise smell in composting toilets boils down to:

  1. Separating the urine from the faeces

  2. Covering faeces in compostable material (there is a wide variety, most use sawdust)

Building your own composting toilet is also incredibly easy. We have been scratching our heads ever since we built it because we can't believe we didn't do it sooner!

Below are the steps to building one, along with the materials needed.

Materials needed:

Step 1 - Creating the box

Your time on the toilet needs to be comfortable, after all this is a space where you will be depositing your bodily waste daily, and if it's a comfortable experience then that makes life more enjoyable. The key to a comfy toilet experience is to consider:

  • Height of the toilet. You don't want your legs dangling, but you also don't want your knees up by your ears

  • Toilet seat. You can go wild here, buy the craziest one you want. Just make it comfy.

We were slightly - read: incredibly - restricted by the choice for height of our toilet due to the area we would be storing it. Our toilet is going to slide out from under our bench seating in our Mercedes Sprinter van conversion, which we happened to build at an impossibly perfect height for us. Which also reads as; an impossibly low height for our toilet. So yes, I'm slightly contradicting myself in Step 1 by telling you to make the height comfortable, and then building mine lower than I would like! 


We were limited by the bench height, and had around 30cm to play with. Not very high, but high enough. Trust me.

Building the frame of the toilet is simple:

  1. Decide on desired height of toilet, and correct width. Remember to include the size of the toilet seat you'll be using. You'd be surprised how wide you will need it.

  2. Cut out six pieces of ply for box size (top, bottom, four sides)

  3. Attach all four sides, and bottom section of ply

Attaching the ply with a pocket hole jig increases the strength of the box, and also hides all the unsightly screws. 



Step 2 - Cutting holes

diy separating composting toilet

You will need to keep the top section of your plywood box loose so you can remove it to empty the contents. You will also need to cut a hole in the centre, to allow all your bodily waste to fall through. 

This is where your toilet seat comes in as a handy template. Position it atop the plywood, open the toilet lid and with a pencil draw around the entire inside circumference of the toilet seat.

Give yourself a little wiggle room by cutting the circle slightly wider than the circle drawn.

Step 3 - To stain or not to stain

This is not a necessary step, but we wanted to give the toilet a bit of character. We also attached handles to both sides of the box, which made it look like a coffin. We now fondly refer to the toilet as the turd coffin. 

Step 4 - What on earth is a urine separator?


Our composting toilet has a urine separator attached to the top, allowing the urine to flow into a separate container from the faeces. This minimises smell, but also makes it a lot easier to dispose of the urine regularly and keep the faeces bucket a lot 'drier' than if it was mixing with urine. 

Having lived with a chemical toilet for years, which we eventually stopped using chemicals in, we can confirm that keeping faeces and urine in the same container smells horrific! Sawdust can help by absorbing some of the liquid, but there's only so much humble sawdust can actually do.

We screwed the urine separator to the underside of the composting toilet lid, at the front of the toilet itself. We also screwed the toilet seat to the lid, so it's not going anywhere.

Step 5 - Buckets for 1s and 2s

The final stage of the composting toilet involves 2 buckets, or containers. One for the 1s (urine) and one for the 2s (poos/faeces). 

At the time building the composting toilet we hadn't managed to find the perfect container for the urine, as we needed a low, narrow, but long container. We have settled for a small pot for now which contains 3.5 litres. We empty it every day.

Our other pot, or bucket, cost 98p from B&Q and we trimmed the top off to fit inside the box. Yes, the toilet is that low.


DIY Composting toilet review

I'm sure you're all dying to know how successful our cheap and easy composting toilet is. And...

It's brilliant!

Using it is as simple as using any toilet, you just do your business and you're done.

Emptying it is incredibly easy; we deposit the urine into the bushes and wrap up the bag for the faeces and pop it in the bin. You could bury it if you fancied (not in the bag), a safe distance away from a water source, or compost it which we will be doing on our land in Portugal.

You may be wondering how often we need to empty the poo bucket, and the answer is every couple of days or even more. You'd be surprised how little room poo takes up! Urine is by far the fastest filler in the toilet, and due to us not having the correct sized container for the toilet yet we have to empty it a lot more frequently than we'd rather. 

We've had quite a few people wondering why we didn't continue with a chemical toilet, and there were many reasons. We didn't like using chemicals for a start, and emptying it was just a massive faff. They smell also. It's just our personal experience. 

Full video tutorial for DIY composting toilet here:


FAQ about the composting toilet:

1. Why is it so low?! 

So it can fit under our bench :)

2. Most composting toilets have urine and faeces in the same container. Why are you separating them?

Keeping them separate allows for us to empty the urine regularly as it will fill up faster than faeces. It can also help keep the smell down if they're separated.

3. Where can you empty it?

You can either bag it and bin it (it's the same as binning nappies, cat litter or dog poo), or dig a deep enough hole and bury it. OR if you have the option you can compost it - we will compost it on our land but won't be able to do that on the road. There are more technical toilets that compost it over a number of months, but for our basic loo we have to empty it instead.