As I did my research on composting toilets I became aware of the overall problem of how modern humans deal with our excrement. We are the only mammals on the planet that combine their feces with their urine in order to dispose of it. These products come out of our bodies from different parts for a reason, that reason being that nature does not want us to combine them. Pretty clear. Yet we ignore the obvious and combine them down a tube using fresh potable water. We then push our byproducts down progressively bigger and bigger tubes into faraway tanks, using lots of fresh water. Then we use even more water to separate the feces from the urine in enormous tanks that smell for miles. We so smart!...
Clearly, the key to proper composting and better disposal of our excrement is to separate the feces from the urine. We can then dry the feces which becomes odorless to humans. The urine does smell but is easily disposable as it does not carry pathogens. That is why peeing in the bushes is not a big deal. If you are on certain medications you do have to be careful where you dump your urine. I invite you to visit http://humanurehandbook.com. There are many other sites and videos on this subject and on composting toilets.
Separating toilets for rvs are pretty expensive, most are well over a thousand dollars. In addition, all the models I found rely on a urine tank that is open to the urinal end of the bowl, meaning that you can smell the urine. The manufacturers mitigate this issue by using a fan to both dry the feces and vent the urine smell out of the rv.
The original toilet was broken and would have to be changed, so I removed it. I decided to leave the black water tank in case any future owner decided they did not want a composting toilet. I had enough room in my toilet area to think about making my own toilet system. So I built the toilet box out of scrap wood to fit my existing space. Then I added all the necessary systems and this was the result:
The custom toilet sits on top of the black water tank flange. I sealed the black water tank with a removable plug. Eventually the top surface will be covered with aluminum also, just like I did the front of the toilet.
To empty the feces bag and urine tank the top of the toilet is removable. And yes, for my male friends, you DO have to sit down to pee...
For the toilet seat and separating basin I used the Separett Privy 501. http://www.separett-usa.net. This is not an inexpensive piece of plastic at close to $200 dollars but they are the only game in town for a preformed separating toilet basin. Here is the seat and separator system:
What I needed now was a way to seal the urine tank to avoid the smell. Obviously could not use a conventional plumbing "P-trap" system since that requires water to act as the odor seal. What I found was a P-trap equivalent that does not rely on water. It is called a HepvO valve http://www.hepvo.com. This little beauty is a tube that has a one way bladder that allows for liquids (and solids) to travel down the tube but then closes to stop any odors. I got mine through Vintage Trailer Supply.
In order to capture the urine from the front basin into the urine tank I cut a plastic funnel to shape and attached it to the HepvO valve. I then cut an appropriate diameter hole in the top of the urine tank to attach the valve. The urine tank has a two gallon capacity and has a vented lid.
The toilet seat urine nipple fits well into the funnel. The urine tank sits in tightly in a cradle made out of wood scraps. It pulls up when needed for emptying.
In order to work properly in a urinal, the HepvO valve manufacturer recommends that the valve be installed in a vertical position. In my situation, putting the valve vertically would have added about 6 more inches of height to my toilet box, which was not feasible. I compromised by putting the valve at a sloped angle by sloping the urine tank cradle. Works great.
Next step was installing a fan. http://www.littlehouse.co was a great resource in my research. The fan has two purposes: remove any smells; dry the feces. I had planned to use the existing black water vent to exhaust the composting toilet smells. As for drying the feces, the key is to have the air flow just above the lip of the bucket, which creates a low pressure zone. This insures that there is constant air flow in the bucket drying the feces faster.
Computer fans draw very little amperage (mine uses less than 1/10 amp) and they are very quiet making them ideal for this application. I decided to get a low flow model. It is rated at three cubic feet per minute. Now that may not sound like a lot but in a small space like the enclosed toilet box it is very adequate since this fan runs continuously. I ran a flexible 2 inch hose from the box interior and tied it into the black water tank 2 inch PVC vent with the fan inline:
Towards the top of the above photo you see the low flow fan horizontal next to the vent connection. While stress-testing the toilet I found out that when the toilet lid is up there is some smell so I added a high flow secondary computer fan that you see on the left side of the photo. This secondary fan runs on demand when you are "using" the system.
Once the fans were installed I was concerned about how much air (3 cubic feet per minute) was being removed out of the trailer continuously. It is such as small space that in a few minutes that fan is going to recycle all the air in the trailer. Less than ideal when trying to cool or heat the trailer interior. I ran a second flexible hose that brings fresh outside air and put that hose directly across and at the same height as the exhaust hose. Thus the air flow is running just above the feces bucket to create that low pressure zone that we want:
In this way most of my toilet exhaust air is fed directly from outside and I am not venting my air conditioned or heated indoor air. The air inlet is on the rear bottom of the trailer:
As of the writing of this blog post I have tested the system for months and it works great. My cost for the toilet was under $300, compared to over $1000 for a factory model.
After billions of years of evolution, and hundreds of hours of hand-wringing, I present to you my dry toilet solution: the bucket!
PS: In case the more squeamish of you are wondering what is at the bottom of the bucket, it is sawdust...This photo was taken when the system was clean....just saying...