Making a close fitting seat for a DIY compost toilet

Here we show you how to modify a standard wooden toilet seat to fit a Kildwick Urine Separator, whilst providing a good seal between the seat and the lid which will help keep odours in and bugs out!

This information is a basic guide and shows how we fit seats. We can’t cover every situation or material, so please adapt to your set-up and use at your own risk!

Choosing the right seat

GL_SEAT - 1It’s important to make sure you get a solid wooden toilet seat – this technique will not work with plastic seats. Composite materials such as MDF may be OK, but you will need to completely seal the cut edge and matching the colour or finish may be tricky.

It’s not essential to have a complete, air-tight seal around the seat because your cover material (such as sawdust or fine shavings) or the ventilation fan, should take care of all odours, but having a good fit around the seat means the flow of air into the toilet can be better controlled. If you are fitting a fan to extract odours, you will have to fit a vent (approximately opposite the fan) to enable air to enter the toilet, otherwise the fan will be labouring too hard.

In this example, we use an FSC certified solid wood toilet seat from a local DIY store – these usually cost £20 or less. You can use the same technique on £50 oak seat too, just double-check everything before you cut the wood!

What you need

  • Solid wood toilet seat (as described above)
  • Good, sharp hand saw (or circular saw/jigsaw if you are confident using one, but a handsaw is quick and easy)
  • Pair of hinges – each side of the hinge should be just less than the thickness of the toilet seat
  • Drill to drill a pilot hole for the hinge screws
  • Varnish or stain to seal the exposed edge

Getting Started

It’s important to spend time working out exactly where the Urine Separator will go, i.e. how far forwards or backwards. If you are using a hinged lid on your compost loo, bear in mind the urine spout might catch the front edge of the toilet box. We can’t emphasise enough how important it is to think about every possibility/problem and try to visualise it before deciding on the location and cutting wood!

1. Remove the hardware






First step is to remove all the hardware. On this seat, the hinges are screwed, and the plastic supports on the seat and lid are also screwed. Some may have clip-on supports.

2. Mark your cut line



Because we’re going to use a hinge on the back of the seat and lid, we need it to be flat and they’re usually curved slightly. Mark a line about 2cm or so from the back of the toilet seat. We mark it on the bottom.

3. Cut the seat & lid!



Now cut the seat across the line. Whether you are using a handsaw as shown or an electric saw, always go slowly and carefully to ensure the cut is clean and straight.

Once you’ve cut the seat, turn it over and lay the lid down. Get a feel for the best position (we bring the lid forwards slightly to have a slight overhang at the front so you can grip it easily to open – bear in mind that there will not be a gap around the edge as with ‘usual’ seats).

Once you’re happy with the position of the lid, mark a cut line and cut that too.

4. Seal cut edges

The exposed wooden edges will be prone to damp and splashing, so it’s a good idea to seal them using a suitable sealer or varnish. If necessary, you might also want to use a coloured stain or varnish to match the seat. Having said that, the exposed wood is at the back and will not normally be visible to the user.

5. Fix hinges in place



Using butt hinges (or any type you want – as long as they work!). Mark the lower fitting and screw into place. We suggest drilling a pilot hole to reduce the possibility of splitting the wood.

Position the lid and fix it in the same way.

6. Fit in place

Place the seat into position and fix from below. Make sure your screws are long enough to go into the seat from below (ie through the material for the top of the toilet and into the seat) but not too long as you definitely don’t want them coming through the seat too!

We’d suggest drilling pilot holes into the seat to avoid it splitting (happened to us once on an oak seat – expensive mistake!).

To help stop urine getting between the seat and the separator, when we make toilets, we also fit a self-adhesive neoprene strip (you could also use silicone) to seal the gap.

7. Enjoy your seat!


GudLoo Divert

Well done you! You should now have a beautiful wooden toilet seat on top of your compost toilet. Have a cup of tea – you’ve earned it!

If you’re feeling proud of your compost loo, why not send us a photo? We’d love to put it on the website to inspire other people to make their own too – just get in contact

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