Design considerations for a home-made composting bucket toilet.
This is my 2c coming from 2 years of living with a homemade composting bucket in a non-air-conditioned 100% off-grid home. Fwiw, mine cost less than $10 to install with just basic framing and a re-purposed seat. All my pics are MIA, but I will post them if/when I find them, though they may be gone forever in an old dead phone...
For starters (or for emergency back-up) a perfectly usable bucket can be fashioned with nothing more than a swim-noodle 'seat,' which is partially slit and snapped on the rim of a five gallon bucket. Set this on a level and stable platform, (you can also string the TP onto the bucket's handle inside a gallon ziplock bag for convenience.) Used in the woods, I would fashion a brace/frame for it by lashing together some dead-wood (2 long/2 short) that I then lash between two nearby trees, and then set the bucket in the resulting square for stability. You can tarp a privacy screen to the trees too btw
At the very least were one to use this set-up in a moving vehicle, you would want some sort of stable frame or support to keep it from siding and/or tipping over in transit (or while in use - Ew!)
While I find this acceptable if I were tent camping in the boonies, or on a weekend trip in an unfinished conversion, personally, I would want to make it look and feel closer to the real thing especially if it were for more than temporary use.
Things to consider in a permanent design:
1.) I suggest designing your setup with an easily obtainable, consistently sized bucket. It sucks when you have to replace your bucket and find that the new one is too tall/short/narrow/wide for your permanent enclosure's opening or for the height of your enclosure. A wire-bale carry handle is preferred. More on that later. All five-gallon buckets are not the same height or diameter, and you will need to be able to reposition them slightly so they work correctly under a fixed opening. Look for one that has reinforcing ribs around the opening. There are square buckets, though they can be harder to keep clean without a liner. Any bucket will do, but some will last longer than others, some are sturdier, and some get brittle over time or with temp changes. Be prepared with a replacement plan and a spare at all times. I do not recommend anything bigger than 5 gallons because weight becomes an issue during maintenance.
2.) After you determine what your preferred bucket will be, use that diameter to choose your toilet seat. Bring a measuring tape when you select your seat! A long narrow seat over a narrow diameter bucket is going to result in a crappy mess somewhere. Literally. Check both front to back and side to side dimensions of the inside dimensions of your toilet seat.
3.) I highly recommend a hinged LID to your fabricated 'bucket box' vs. a front access. This is so the bucket can be lifted out. It is less accident-prone than a front access hatch where the bucket will accidentally tip when you reach in and grab it or when you slide it out to empty it. (dont ask how I know this...) The liner is more likely to snag and tear when removing it from the front because of the minimal clearances. You should allow enough room in your design of the 'bucket box' including its hinged access lid, to clear the handle when you reach for it and when you swing it up to a carrying position. Also allow enough clearance to reach down for the free edges of the liner bag without getting your hands/arms 'stuck' while manuevering around the bucket. Fwiw, it's much 'nicer' to lift out a bucket by the handle vs. having to grab onto the rim which may not be so clean. It is also easier to secure the liner when replacing it or when sealing it for dumping when it is not inside 'the bucket box.' A handle on the bucket is not really necessary if you always plan on using a liner and plan to replace it while it is in 'the box' however a bucket with a handle makes a very convenient transport container to carry your sealed liner/trash bag to the dumpster with no chance of bag failure in transit. <ewww>
4.) Determine a comfy height and position for your seat. A toilet seat mounted on a box needs to be fairly close to the front edge so your legs clear the front edge of the box (think portolets) BUT you will need a bit of extra space towards the back wall compared to the front. Do NOT center the seat, front to back, or scrimp on the depth. You want to be sure when you raise the seat to add sawdust, it has enough 'lean back' to stay put, or some sort of catch to hold it in place while your hands are busy with maintenance. Same thing applies to the box's top access-hinge. The top of the box needs to be able to tilt back (or be secured in the 'up' position), with the toilet seat AND lid attached whenever you empty/change the bucket. If it doesn't stay up securely when emptying, you are asking for a mess when the lid falls while you you are attempting to empty or remove the bucket.
4.) To determine the preferred height of your box- first, you do NOT want the lid to rest directly on your chosen bucket and bear all the weight in a permanent installation or you are asking for container failure in a short time.
-You don't want a big gap either- another mess waiting to happen.
-The weight of the box's lid (and the weight of the person using it) should rest on something very sturdy like 2x4 framing and maybe a front lip inside the box, or an overhang over the front edge of the box, depending on the sturdiness of the material you choose to use for the top.
-Obviously the design height of the box cannot be shorter than your bucket, (unless you have a sunken floor) but it is quite possible you may want your toilet seat higher than the bucket is, so design a plan to elevate the bucket that will reduce the gap between the bucket lip and the inside of the hatch. I would venture 1/4"-1/2" gap is the goal.
-A compressible rubber gasket which is easily cleaned, and used to fill this void for an air-tight water-proof seal would be ideal.
-Finished height is ultimately entirely dependent on your preference.
-Consider any sagging/bowing of the access lid when it has a heavy weight load and design accordingly. Don't allow this extra stress/load to be carried on your bucket's rim.
-Incorporating a hook or ledge that the bucket's handle can rest on, away from the side of the bucket, will keep it away from the potential 'danger' zone of any accidents too, but this handle-rest _may_ not be feasible when using a liner because you won't be able to secure the over-hanging bag securely on many bucket styles when the handle is perpendicular to the bucket's side.
5.) Design your containment box and/or framework using your measurements. Things to consider:
-Shoot for a perfectly secure and consistent placement for the bucket, but allow for variations in bucket diameter and height with with something adjustable should the need arise.
-allow an inch or so leeway in all directions for bucket adjustments should you have to substitute a different sized bucket at any time in the future.
- Methods of securing and stabilizing the bucket are endless, but I would recommend some sort of framing on the underside of the hinged top. This frame would slip/fit over the outside of a properly positioned bucket and extend about one inch over the bucket's rim. I would suggest a front latch on the access cover that only engages when the bucket is properly positioned inside this 'frame' as well.
-The bucket's lip is THE most important position to keep stable and properly positioned during use to avoid a mess.
-Framing the bucket lid this way is dual purpose. Because this positioning guide is attached to the lid and will lift out of your way during routine maintenance, it keeps structural details out out the 'line of fire' and limits structural details inside the box that would be more difficult to clean in the case of accidents/spills.
-You WILL need something in the base to consistently guide positioning and keep the bucket from sliding or shifting in-transit. I would start with something adjustable/temporary until you had good trial run to assess the perfect positioning for your set-up.
- All toilet seats do not always fit perfectly over a five gallon bucket, nor are buckets consistently sized between brands. Should a replacement bucket be a different height or diameter, always allow for minor size discrepancies in your design, and the ability to adjust your 'bucket stabilizers'. Allow for the tallest bucket height possible in your original build design. You can always add a shim under short buckets.
-design and create (and line) your 'bucket box' with something waterproof/resistant and easily-cleaned in case of accidents, spills, misses etc.
-Strive for a minimum of angles and exposed structural details that need to be cleaned around, or that could hide 'stuff'.
- Do NOT use absorbent or unsealed wood, USB, or plywood - you do NOT want an outside surface OR interior surface that can absorb anything. Nor a texture that can catch and contain urine or feces, or their odors, nor anything that can swell with moisture. (I am planning on lining mine with a waterproof fiberglass mat unless a better alternative comes to mind.)
**You may want to consider a two compartment box; one compartment for the humanure bucket and one for the sawdust, which would preferable be higher than the bucket box's surface- this helps to eliminate accidents of liquid run-off from leaking into the sawdust (shower spray/urine/condensation or whatever) . An angled lid is also a plus for the sawdust container if it is near a sink or potentially any shower overspray.
-consider ease of refilling your stash. It is much nicer and less messy to fill a bucket or container with sawdust while outside your rig where you can snap on a lid or secure a liner-bag _before_ you walk through your living areas.
-Ideally you would have the ability to place said container/bag directly into its storage compartment in your bathroom without transferring the contents.
-If you transfer sawdust from one container to another in your bathroom, can you see the dust cloud and potential for a mess? You do not want to try this!
***Things to remember***
- if using a liner, you will need some manner of securing the bag so it doesn't slip into the bucket as it fills- bungee? Large heavy rubber band?
-The sawdust needs to be dry, so whatever containment method you choose, it needs to be impervious to water, moisture, and shower humidity. A large damp mass in warm humid temps will grow mold eventually.
-I would recommend storage for two somewhat smaller containers of sawdust vs one large container to alleviate the potential of moisture absorption. Consider it like a back-up roll of TP. One for daily use and one for back-up. The back-up would have no chance of moisture infiltration and would remain sealed until it's needed.
-The simple low-end/low budget solution for sawdust=a trash can with a tight fitting lid and a plastic liner that can be sealed as a back-up moisture barrier. It really doesn't *have to* have any enclosure or box, just secure it to a couple of rings/hooks for stability.
-***large square kitty-litter containers, or square plastic animal-feed containers are great storage containers for sawdust. They stack and fit together nicely with minimal wasted space. They are a convenient size too. (I got friendly with the crazy cat lady down the street for a never-ending supply)
*bonus*- I could easily fill these right at the lumber yard/carpenter's shop and transport them in any vehicle. (Vs the pick-up bed for large-hauls)
-you will most likely have a sawdust trail between the sawdust container and the humanure bucket. You want to minimize the distance the sawdust scoop travels from its storage place to the destination bucket.
-I highly recommend that the path is NOT over floor space or else you are destined to be tracking sawdust all over.
-Ideally the opened sawdust-container lid would span the distance to the humanure bucket's opening so any sawdust spills will land in either bucket, or on the underside of the sawdust lid- and then back into its own container when you close the lid.
- Until you find a scoop that works well for you, I suggest a commercial ice-scoop, like bartenders use to make drinks- the kind with the higher square-ish sides. Don't over-fill and spill it! Better to scoop two smaller scoops if necessary for less mess.
For a 'luxury' design, I would add:
-a small floor drain inside the 'bucket box' for occasional rinse-outs *with a removable screen to catch errant sawdust.
- an airtight fit with some sort of gasket between the bucket and box lid, and again between toilet seat and box lid and the toilet seat and its cover. (Rubber gaskets? silicone bead? I'm sure there is something groovy to use!) The main purpose of this is to exclude any flies/bugs that may get inside your rig. Odor is not usually an issue.
-The seat could rest directly on the top without those usual spacers, but that does present a potential 'pinch hazard'. Best to leave a gap at the edges of the seat.
-Using a swim-noodle slit partially through and fitted over the rim of the bucket and under the top hatch might work to seal the bucket to the hatch, but have not tried this personally. I'm not too sure about the ease of clean-up of this with an unlined bucket, but with a liner, I think this may be perfect, plus it would alleviate friction/wear on the bag if the bag was draped over the noodle-covered bucket rim. You would have to allow extra height in your build for this though.
**a urine diverter (mine will have one for sure!)
These will extend sawdust use/replacement considerably and obviously decrease moisture too. A portapotty-style urinal for men would be great! The more you keep the sawdust dry, the less odor and moisture you will potentially create. Decreasing urine also decreases the weight and frequency of trash/compost runs and makes less chance of lining failure during maintenance due to excess weight.
-The urinal could be also be tied to the "rinse out" drain and/or your holding tank.
-There are various methods to divert urine for women, but none so simple.
In a pinch, I have used wood shavings sold for pet bedding from a pet store/farm store when I couldn't get dry sawdust. It is not as absorbent as sawdust, but (especially with a urine diverter, ) it is a totally usable/acceptable alternative, albeit much pricier than the (usually free) sawdust. I always kept a bag on-hand in case I couldn't get a load of sawdust when I needed it.
I hope these ideas lead to a happy relationship with a very inexpensive toilet option. I'd love to hear any other ideas for improvements too, as well as any specific parts that y'all might find that suit some of the vague ideas I threw out there to consider.