This topic deserves the hundreds of books written about it, and the many creative ways people dispose of their human waste. I'm not squeamish about this topic and I'd like to be as straightforward as possible so you can better understand how you want to design your system and what each type of system would need.
Most Recreational vehicles here in the USA have a normal flushing toilet like what you have in your
home, and this is called black water. This waste is stored in a large
container under the vehicle that you would empty when you drive up to a dump station, campsites, etc. that is designed for sewage disposal. Usually you would have a 4 inch diameter hose that locks into place on the container and is then drained through gravity and a black water pump into the disposal connection. Most of the time people empty this container weekly / bi-weekly and you have to pay for this service. There is also a constant upkeep of adding chemical agents that break down particulate matter in the tank and having to service the pump occasionally. I'm heavily against wasting water for this and started to look into alternatives that were available - like dry / composting toilets.
Firstly, the process of composting is the natural decay of matter through biological mechanisms like fungi, worms, sunlight, etc. and is a great way to break down items in an ecologically beautiful mindful way. The actual process of composting takes months to years, and unless you have land to dump your waste and go through the complex design process of composting human waste, then you're not actually "composting" your waste. The type of toilet that many people call a composting toilet used in tiny homes and RVs are actually a dry toilet - it simply separates the fecal matter and the urine so as to not create sewage, but there is no actual composting going on.
Sewage is the combination of fecal matter and urine, and the combination and interaction of these two are what creates the awful smell we associate with sewage. In a black water tank these two are mixed and disposed of together, while a dry toilet separates and disposes of these separately to eliminate the possibility of them mixing/interacting and creating sewage. This is the main appeal for composting / dry toilets. When you eliminate the ability of these two substances interacting, there is never a chance to create sewage and therefore it shouldn't create any smell (if done properly). Also, you don't waste water with your toilet either which is another bonus.
There are companies that sell composting toilets, averaging $400 to $1000+, and personally if you were going to spend $1000 on a toilet then you might as well buy an incinerating toilet and not worry about it at all. But rest assured you can build one yourself, as long as the main idea of the toilet remains.
Building a Dry Toilet:
The main idea behind this type of toilet is if you separate the fecal matter from the urine, it stops the creation of sewage and allows the fecal matter to dry out rather quickly - eliminating any odors coming from your toilet. Usually the toilet is made with a large bucket to collect the solid waste, a urine diverter (like a half - funnel) that covers part of the seat opening to collect most of the urine into a separate container, a fan to help dry out the container, and another separate container to hold your drying agent for the solid waste (coconut coir, pine pet bedding, wood shavings, etc.). The idea is that after you use the toilet you would cover up the solid waste by covering it in some type of porous material to dry out the surface area of the waste - any surface area of the waste must be covered by some type of drying agent; this is also why the urine is diverted away from the solids as it wouldn't allow the fecal matter to dry out. Inside the toilet cavity would have a vent connected to a fan that increases airflow to help the drying process, and is definitely necessary. There are stand alone toilets you can buy that do not include a vent / fan, and do not dry out the contents well enough to stop odors from being created. A simple 12V computer fan is what most people who build their own use, and they're fairly cheap. I should note that this fan would run constantly, and it is a power draw (although pretty small).
Eventually you would have to empty your urine container, which is as pleasant as it sounds. Usually people dump their urine into a toilet, porta-potty, etc. Although urine is almost sterile, it's not something you would want to collect into your grey water storage unless it's heavily diluted. The solid waste is, most of the time, thrown away into the trash after it has completely dried out in a biodegradable bag. I've heard that some people bury it, some people burn it with a mini rocket stove, etc. The worst aspect of a dry toilet is disposing of the waste in a mindful way - which could be difficult depending on where you're living. More and more people are deciding to utilize a dry toilet because of water scarcity, and although that's a great thing for our cultures to be aware of, the process of disposal hasn't caught up yet. At least if it's completely dried out then it shouldn't contaminate surrounding trash if compacted. In the future I'd like to burn mine in a dual-combustion rocket stove type of thing. I'm always looking for better options than this, but you should know that this is the most common way people dispose of it.
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It's fairly straightforward when you know how it works - as long as your toilet design follows this principle then it should work for you like it's worked for people all over the world. You need a large container for the solid waste and absorbing material, a urine diverter, a container to hold the urine, a venting system, and lastly a toilet seat to sit on.
I first started to design my toilet based on the area I allocated for it in my bathroom. I wanted mine to be like a large bench with a lift up seat, have a large urine diverter that covered the whole bucket (which they don't make), have the urine diverted to a separate container, and include a fan that is vented to the outside through the wall. When I measured our toilet at home, the top of the seat reached the height of 18 inches, so that's the height I designed the compartment to be (with the toilet seat on top of the lid as well - make sure that's all included in your measurements.) I made the width the whole bathroom width, and the depth is the depth of my particular toilet seat I bought. As long as a toilet seat can rest in that space comfortably (not too much space in front) and your shoulders don't hit the wall when you're sitting on it, then it'll work great.
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| Here's the toilet so far - built out of 2 x 4s and 2 x 2s, I paneled the inside with extra kitchen wall / flooring planks so it would be washable if needed |
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| The urine diverter swings from a pivot point to lock in place and land inside the bucket (slightly) |
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| Here's when it's "locked" in place. I put a small screw into the lid to act as a stop, and that bracket on the left hold the diverter against the screw |
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| when you need to go, you would lift the seat up and swing it over |
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| The urine diverter covers the entire seat. The toilet seat goes slightly past the edge of the bench lid - if there's too much space, it'll rub against your thighs when you sit |
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| Here you can see how the toilet seat sticks out slightly |
Composting Toilet Components:
-MDF for the bench lid
-external rated polyurethane to seal the lid - needs to be washable & chemical resistant
-5 gal bucket
-urine container
-a 50gal drum Funnel - repurposed as a urine diverter. I used a 4-quart funnel, this one actually, as it's chemical resistant and it's the same diameter as a normal toilet bowl (11.7" - 12"inches). The thread on the funnel is designed to screw onto a 50gal drum, so I bypassed the thread with PVC pieces. I just hammered the PVC piece over the funnel threads, and (I believe) I added PVC cement as well so try to seal them - it hasn't leaked.
-PVC fittings to fit over the urine diverter - adapting from the funnel thread to a compression thread, leading to your urine container.
The Urine Diverter:
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| 2" PVC slip x 2" female thread, PVC welded to an adapter that converts down to 3/4" pipe thread. Then I used that brass union to convert from 3/4" National Pipe Thread to 3/4" Garden Hose thread so I could use a standard dishwasher fitting - 3/4" Garden Hose Thread to 3/8" compression. |
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| I drilled a hole through a rubber plug so the vinyl compression line can run through it, straight into the urine container. The plug was the exact size of the hole for the container |
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| I used metal strap to hold two L brackets against the side of the diverter - I didn't want to screw into it. I tightened it down with a bolt to hold it with tension. Maybe some super glue wouldn't hurt either |
Using a 12V computer fan as your toilet fan:
Usually there are three wires with a computer fan; Positive, Negative, and a third wire that controls it's speed. Usually in a computer the fan would run at different speeds depending on how hot the system was getting, which is controlled by varying the voltage to the fan.
Only using the positive and negative wires would give you a constant full speed when direct wiring a 3 prong (three wire) computer fan. If you wanted to be able to change the speed then you could use a potentiometer to vary the voltage to it and slow it down. These are usually turned by hand to different voltage rates which would in turn slow the fan.
The reason that some people add in a potentiometer is because a normal 12Volt battery can idle as high as 14Volts while it's charging. So if I have a changing voltage with my batteries, could I still use a 12V fan?
Often times equipment like computer fans that are low-voltage DC will actually accept a range of voltages, so long as it's close to it's "rated" voltage. Most computer fans that are rated at 12V can run on higher voltages; it'll just run faster essentially. Sometimes a fan will require a constant 12V regulated supply, but the manufacturer should specify it on the product. (Ideally. You may have to ask.)
So we know a fan will run faster at higher voltages, but what is the acceptable range? Should I regulate the voltage to make sure it stays at 12V? Regulating the voltage gets complicated when the source and the output voltages are closer than about 2 volts, because regulators need some headroom to work with. Aside from potentiometers, you could use a buck converter (step-down converter) that could lower the voltage down to a consistent 12V, but usually the smallest difference for a buck converter to work with is 3V - so bringing it down from 14V to 12V is just too small of a difference. You could solder together individual diodes that step it down when it's that small of a difference, but that's somewhat of a pain if you don't need to.
Most automotive batteries sit around 13.8V; which is worryingly high if your device wants a regulated 12V input, but it's annoyingly low if you want to regulate it to 12V, even with a buck converter. I've seen people run tests with 12V fans running on 16V and do fine, and apparently even higher voltages before the bearings started to break. I don't think the voltage difference between 14 to 12V would be enough to damage your fan - but for this reason I bought two.
[UPDATE: I run my little toilet fan 24/7, and usually the batteries idle at 12.6V. Sometimes they get as high as 14.8V when I'm charging them, and the fan doesn't seem to care at all. 16V may be too high, and I wouldn't want to run the fan at 14V+ all the time, but it does perfectly fine at varying voltages. The only time I can hear it stressing/whirring is when it's windy outside and there's a back-flow of air coming back in through the vent, assumingly pushing air against the fan in the opposite direction and making it work harder.]
When the fan is on, there is a very soft yet brisk breeze inside the compartment when pulling the air out, around 12.6V. (normal resting voltage)
I bought my fans and the vent duct from CoolerGuys online- who I highly recommend.
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| Most fans run around $8USD - I picked ones with the highest CFM (Cubic Feet of air per minute) at the lowest sound decibel (an average conversation is as loud as 60dB - one of the fans was 23dB at 32CFM) |
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The face of the vent cap sits flush against the wall with an extruding 4inch diameter tube that goes through the wall into the toilet compartment. This is what the ducting attaches to; Once there's air flow it pushes up the leavers in the vent letting the air out.
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| I used silicone to attach this screen permanently to the vent |
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| This is the end connection for the venting tube from the fan that will slide over the vent pipe |
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| The white pipe will slide between the bolts and the wood on the inside seen here, and I'll fill in any space with caulking and then spray foam later on |
All of the wiring for the fan, run in conduit, and the flexible venting tube connected to the wall vent outlet. That white metal disk on the floor is the actual hole I made in the wall with a jigsaw.
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| I hammered in the wood piece over the vent and sealed any space with clear silicone. Here you can see the basic run for my fan wires I ran in blue conduit (sorry for all the weird colors - I only had black and green wire! Make sure you mark them correctly) |
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| After it was all dry I filled it in with spray foam |
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| Here is the beginning layout for the toilet. I screwed the fan into a plywood piece, and added a small rocker switch to turn the fan off and on. |
Paneling the inside:
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| That corner piece with the handle slides up and out. This lets me reach the wiring and the vent if I need to |
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| Practicing the diverter movement |
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| I need to secure that urine container somehow.. |
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[UPDATE: August 28th, 2024]
So I've finally moved into my little house, and one of the first things I had to practice and re-work was the composting toilet. The design itself works great, but I ended up putting in a larger urine container (1 gal), a more flexible compression line to the container (which I might re-do again), and I added a plastic collar to the 5-gal bucket so the edge of the bucket is as close to the toilet seat as possible.
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| The blue plastic collar is a dollar store bucket I removed the bottom from, and I cut a portion of the side out so the diverter could rest next to it when the seat was down |
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| The collar brings the bucket height to 1/2 - 3/4 inch below the toilet seat, without having it be rigid and difficult to remove the bag, etc. I screwed the bucket into the floor and walls so it stays still |
There are some tricks to using the toilet that makes it work: If you're doing it right, it shouldn't smell (outside of your toilet compartment that is)
I keep a small half-gal container of water in the bathroom, as well as a spray bottle with Lysol Concentrate and water mixed together. I use both of these items when I use the diverter; After the urine drains down you'll pour water down afterwards to rinse it, and then spray the whole diverter. It doesn't have to be very much. Usually the liquid in the diverter will evaporate on it's own, so you don't have to dry it. This stops any urine smells you might get, and it keeps it very clean. This does fill up the container faster, but I empty my urine container every morning to make sure it never fills up too high. **Make sure you do not use a bleach-based cleaning agent to spray down your diverter, as urine contains ammonia and bleach mixed with ammonia creates chlorine gas, which is toxic.
Also, because the diverter falls into the bucket when it rests (which has never gotten dirty btw) the compression/drain line has a steep p-trap like design that has to come back up out of the bucket, and then down into the urine container. Sometimes I have to lift the whole seat up, and this raises the line enough to let gravity drain it. Thankfully it only takes a couple seconds, but that is a downside. I could cut a slit in the side of the bucket to remove the p-trap, but I'm not sure I want to remove that.
At the moment I'm using a fine pine shavings mixture I bought at Tractor Supply
I naively thought this was a month supply, but it might be more like a 3-4 month supply. (It is compressed into that block shape). This does work good as the drying agent, but when it's wet/damp it does have it's own smell. I keep the toilet fan on at all times to overcome that, and it works perfectly.
When I use the bucket, you have to make sure to cover any waste with your drying material before you drop in your toilet paper, as the toilet paper bulks up the container too much and it won't be able to coat it and dry it out if it's covered by toilet paper. If you're having smells from your container, this is probably the problem. This takes a little bit of practice. I usually use a full 1 cup measuring cup each time, but sometimes I double that. (I'm still tinkering. maybe I'm using too much. it works though!)
The most important thing is to limit how much liquid / moisture is in the waste bucket, and for women this is a little more challenging as (usually) we may go #1 and #2 at the same time, and this is not something you can do with a composting toilet. Also, any period-related products cannot be thrown into your waste bucket. They need to be thrown into their own small bag, and disposed of separately, so make sure to include little doggy bags or something. Either it was the acidic PH, or the moisture content, I don't know but don't attempt this as it won't work.
I bought a cheap 1 cup measuring cup from the thrift store and keep it in the pine shavings bag, which I keep on the floor in the bathroom. If you need to use the shower, you can move the bag. (not keeping the drying material in your toilet compartment lets you store toilet paper in there, baby wipes, etc. which is much more helpful.)
I read about an older couple one time talking about their composting toilet, and the wife had mentioned that her husband and herself only emptied their waste bucket every week or two weeks, and the urine container every week. Either I need to cut back on how much water and toilet paper I use, or this is not realistic at all and I'm unsure how they're accomplishing that. I would say I empty my waste bucket every 3 days or so, and I empty my urine container every morning so that it never has a chance to overflow. I've tried to lightly compress the bucket contents to make more space, but my diverter also lands inside of the bucket, so it actually can't fill up all the way. So I suppose the cost of having a full bowl diverter; the capacity of your bucket is diminished. I'm very happy with how well it separates the components, it doesn't smell at all - even as quickly as a couple minutes after using it. The only time I smell it outside is if I'm standing directly under the vent, otherwise it's not noticeable. (or no-one has said anything yet.)
The 12V fan has worked awesome - I highly recommend getting a fan that has the highest CFM (cubic feet per min) airflow rating you can find, at the lowest decibel rating so it's as quiet as possible. I've seen the voltage on my batteries climb as high as 15V when bulk charging and that fan was whirring real fast haha. I did blow an in-line fuse for it twice, as it pulls 0.33amps and the smallest I could find was a 0.25amp fuse, so it only really pulls it's max power rating when it's running at max speed. Otherwise I turn it off if I'm charging it, like with a generator (or in my case the inverter / charger.) I've considered getting a small voltage regulator for the fan and wiring it directly, but it honestly seems to be doing fine so I wouldn't worry about it too much.
I wanted to use bio-degradable bags for the toilet, but it seems they degrade when in contact with liquid, so I didn't try them yet. The drying agent works well though, so I'll try that pretty soon here.
I've waited a long time to post this page as I wanted to really try it
first, and I've never seen a design with a full-bowl diverter. I
honestly think it works really well, and maybe you could build and
improve upon this design. At first it was annoying to have to stand up, lift the seat and hold it, move the diverter over and lock it, and drop the seat again. Each time. But now I have the habit down and it's much less time consuming. If you do try this, let me know!
There are a lot of great books written about this topic, like The Humanure Handbook by Joseph C. Jenkins, that really go into depth on the topic if you're looking for something more long-term and off grid. Otherwise I hope what I've been trying may give you some ideas, or maybe you can improve upon the design yourself. Thank you for reading and feel free to leave a comment or send me an email on my contact form. Good luck and happy travels!
Sincerely,
Kelli
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