Yes, it’s the compost toilet update. So, does it really work?

Yes, it’s the compost toilet update. So, does it really work?

Compost toilets: do they really work? In answer to that question, it’s really too early to tell…

Welcome to those who came here expecting interviews or book reviews, or those who have stumbled upon this website entirely by accident. Let me explain. I live on a boat. This means that I am far closer to the elements of living – such as where power and water comes from, and where human waste (or shall we call it humanure..?) goes – than might be the case were I to live in a house, connected to the National Grid, the Mains and the Sewage System. No flushing for us! Not any more.

This post may roam into musings about the state of the world and the finer points of urine separation theory, but essentially it’s an update on how I built my toilet and how the first week of this brave new world has panned out. That was not supposed to be a pun, by the way.

If you have never considered building your very own urine separating composting toilet, you might be surprised at how excited those of us who do get at the very thought. Picture my boyfriend and I sitting in a lovely Lancastrian  tapas bar, waiting for the lightly battered whitebait, the bread, the olive oil. Picture me sketching my toilet design on the napkin. Picture his face. Romance at its very best. I did wonder if he’d ever come to the boat again… My enthusiasm for the project tends to attract odd looks all round, not least from my children. Who are also very good at coming along to see what I have done without entirely managing to conceal the humouring expressions on their faces. (I don’t mean, of course, that I take them along to see what I have done in the toilet, just the construction process. Duh!) My friend Kate understands, which is just as well. She came to spend the day and be my advisor, measurement double-checker, extra pair of hands and all-round cheerleader. Without her, I’d still have all the constituent parts sitting in a heap in the corner of the bathroom.

So, to the process:

Stage One: Buy a compost toilet starter kit

E.g. the Separett Privy 500 from The Little House Company , an:

“economical DIY urine-separating compost toilet kit – an ideal starter kit for those who want to build their own system.”

DIY urine-separating compost toilet kit


Stage Two: Planning

Draw up the plans. Check them. Check them again. Line up pieces of paper to check that the seat will fit and the bucket will fit and the pipe down from the separator will fit. Check again.

Stage Three: Prepare Materials

Prepare the MDF boards on which the seat shall rest. I am a) hard up and b) eager to reuse and recycle as much as possible. I got the MDF boards from the scrapstore in Blackburn, which was great. MDF is, though, not ideal for use in a damp environment such as a boat, being prone to absorption of water and swelling. In order to minimise this, I primed the pieces with PVA, covered them with a layer of papier-mached newspaper and then finished with yacht varnish.

Stage Four: Build framework

Attach side pieces and hope that they fit. It was quite important to me that they did, because the finish on the MDF was in place and I really didn’t want to have to make any changes. I’d had to move the radiator along the wall before I started, and it turned out that I hadn’t taken the pipes into account when I’d cut the bottom corner of the left hand piece. However, there was a piece left over from the old toilet structure which fitted that side down to the last millimetre. That’s the piece that’s brown rather than newspaper-y. It’s also a bit stronger, which is good, and the side that will come out in order to reach the bucket. So, all in all, a useful error.

Basic framework of the compost toilet

Stage Five: Check carefully

Check the dimensions of the top piece before you cut, and make the necessary adjustments… Then repeat PVA, papier mache and varnish. Then fit.

The completed compost toilet

Stage Six: Realise that the bits inside don’t quite fit…

Kate, my support act, had brought round a bucket that seemed perfect, but once the framework was complete, we realised that it was too wide. Kate and her husband, James, run a homebrew shop. The 20 litre fermenting bucket looked ok, but when I got it home, it was too tall. Goldilocks, eat your heart out! Then, whilst I was out walking the dog, I spotted an empty vegetable oil tub discarded in a field bordering the towpath. It was just right…

Stage Seven: …and now for the urine separating bit

Some time ago, I’d picked up one of those water cooler bottles, which had seemed like the ideal thing for collecting the liquid. I knew there wouldn’t be room for the bottle in the bathroom, so my original plan was to have the pipe running around the back of the toilet and through the bulkhead into the bedroom next door. Because my daughter would be fine with a pot of wee under her bed. However, the pipe obviously needs to be going downhill from the seat to keep things flowing, which would have meant having to make a hole for the pipe at the bottom of the bottle. Not ideal. Plan 2 was to use a 5 litre water bottle with the outflow from the seat going directly in without the pipe. Again, it turned out that the bottle was too tall. What to do next? Have you ever walked through a supermarket eyeballing the shelves for containers of any sort that might just be the right size to collect your urine? Thought not. But the Asda basic 5 litre plastic storage tub turned out to be ideal. It even has a little snapback lid so that a short length of pipe can direct it all through 🙂

Compost toilet: How it looks underneath


So far, so good. We’ve been using the new system for a couple of weeks. I’ve gone for the sawdust covering approach in the bucket, and there has been absolutely no smell. Amazing. I knew this was the theory, but part of me couldn’t help expecting something a bit stinky. I did plan to fit a vent pipe, but as this would involve cutting a hole in the steel roof, I’m going to see how things go before jumping in there. If the sawdust means we don’t get whiffy, then I won’t bother. Positioning on the seat needs a bit of thought to make sure everything goes to the place it should, but that’s hardly a difficulty. Three of us fill the 5 litre liquids container in a day, and the solids bucket will do at least another couple of weeks, I reckon. It’s aesthetically nicer than the Portaloo, and MUCH less offensive. And I am so happy that I will never have to empty that sludge ever again!


If you want to see how others have approached the construction of a similar toilet, here are a couple of links. Martin at The Little House Company has chronicled his experience of installing a compost loo here, and also has loads of related info. The Little House Company is also the best place to buy your own kit, and the only place I found in the UK to sell the separating seat.

My own post about the reasons for choosing a compost loo can be found in the ‘Living on Antioch’ section of this site. And I want to direct you again to the amazing Duchamp de Loo via Appropedia. Truly a loo of beauty!






  1. Paul Smith
    12 Dec 2012

    Hi Sarah,

    Would you be interested in answering some questions for the Case Study section of my site? I have over 6,000 subscribers who are interested in living on board (as I do too) so your answers would be of great interest – as would the results of your DIY compost loo project.


  2. Anna
    27 Jan 2013

    Hi Sarah,

    I also live on a narrowboat and have been somewhat obsessing over sorting out one of these DIY toilets since we saw our neighbour’s non-DIY one. I have been putting the project off due to the cutting a hole in the steel issue, so am really interested to hear of your alternative approach – it would be great to hear how this is going now you are a month further down the line.



    • Sarah
      27 Jan 2013

      Hi Anna,

      It’s all going well so far! The only smell issue I’ve had is urine getting trapped between the polystyrene seat and the plastic separator part (I think this is maybe my son aiming wrong…), so have to clean pretty often just there. Maybe worth checking back once the weather warms up in the summer, but the sawdust really seems to be working. Would recommend the whole thing. What system have you got at the moment?


  3. Jorge
    1 Apr 2013


    I am considering buy a boat, and a compost loo looks like will solve the toillet point, but since a boat has not a backyard to use the compost you get in the bucket, what do you do with it?

    Many thanks

    • Sarah
      1 Apr 2013

      I’ve only been composting since October, so haven’t had to decide on that one yet! Find a friend who wants to enrich their garden, I guess 🙂

  4. Becky
    18 Aug 2013

    Hello Sarah
    thanks for this post, very informative. I may have missed something, but what do you do with the urine you collect? And how do you source your sawdust?

    thanks and all the best to you and yours

  5. Deborah
    6 Sep 2014

    Hello. As you are now a couple of years along from your original article I expect you are an expert now. I was wondering how it has all panned out (pun intended)?
    Also I have read of activators and worms elsewhere…did you need any such additions or simply sawdust ?
    Thank you for sharing your experience.

    • Sarah
      8 Sep 2014

      Hi Deborah,

      Thanks for getting in touch 🙂

      Having the compost loo has been brilliant, with very few downsides (if you are comparing it to a pump out or cassette system). Although I’ve also become a bit of a bore on the subject of clean and expensively treated water being used to flush our Western systems, and the unsustainability of this worldwide…

      However, getting back to basics! I just use sawdust, although I am quite interested in trying out worms, just haven’t got round to it. As you say, I’m nearly two years down the line, and my first compost bin isn’t yet full! And it has a flourishing colony of mushrooms (I leave them there, flourishing away).

      What sort of environment are you looking at: house, boat, cabin?

      • Deborah
        18 Sep 2014

        Hi, Thank you for the reply and sorry for my tardy response. We are on a narrowboat. Been making the seat (other half is fitting it now in the style of a victorian wooden seat – very posh ;-).
        That is amazing 2 years and it just keeps breaking down on its own? Can’t wait to get ours sorted as, like you say, the cassette toilet is a vile fortnightly experience. Out of interest have you found any good smell control for the liquids…I read that vinegar can be good and was going to try that. I think we are going to keep container size small to be easy to carry but it would be nice to have the option of doing that less often too.

  6. Barrie Evans
    29 Sep 2016

    Okay you have grabbed my attention for a solution to my garden room toilet facilities.
    One thing I am not getting my head around is the liquid waste.
    Assuming that it all goes into the same riceptical or does it?
    Whatever, how is it dealt with?

    • Sarah
      7 Nov 2016

      No, the liquid is separated into its own container, therefore more or less eliminating the smell factor. It can be used directly on the garden, or poured away. If you are building the toilet in a garden room, then a soak away might be the answer, where the urine is pumped outside (using a small, on demand pump), draining into a gravel patch. If you’re on Facebook, this is an excellent group for all compost-related issues! Good luck, go for it!

  7. Bob Viscount
    24 May 2017

    Hi Sarah
    We have a sailboat and a camper and originally used POO Powder with composting bags but decided to go with a composting toilet. We consider it a desiccating toilet as on the boat we will have nowhere to compost. We are currently using a separret 500 as we could pick up a toilet seat at the habitat for humanity store. We are using coco-coir as a medium as it is compact for travelling. I am glad we built the prototype first as it has given us options in determining the final design and all parts are reusable. We are quite amazed at the lack of odour as we had used the bag and powder method before. Keep up the good fight, and to any out there considering this, build a thunder box and try it out. you will soon be building a permanent installation.

  8. John
    7 Aug 2017

    thanks for all the advice – there are more urine separators about now (see for example which is a bit cheaper though maybe not as nice. Doesn’t have a seat. They recommend urine on gardens in 1:10 ratio. Just saying.


    • Sarah
      14 Aug 2017

      Yes, there are a lot more options out there now, which is great. When I built this, the Privy was the only option really. I’ve recently done a rebuild using a separator from these guys, who have some really interesting design ideas:

  9. Alan
    26 Jan 2018

    Sarah. In your previous information you included the dimensions now I am ready to start I can’t find them could you please give me the height. Length and width thanks Alan

  10. Celeste
    3 Feb 2018

    Have you tried using Bokashi along with sawdust to compost the solids?


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