I definitely prefer boondocking over crowded campsites. As such, a black tank is a hindrance beyond an inconvenience. All that water, holding capacity, and weight wasted on simply flushing a toilet. The obvious solution is a composting toilet, but the market leaders require maintenance that I feel is unnecessary (mainly, a small urine tank you have to empty by hand, cranking a handle to stir up the solid waste, and finally, disposal of solid waste).
Some composting toilets allow you to plumb the urine diverter to the gray tank. That’s a good idea (no dumping a urine jug).
At the time of my build, I was surprised that there didn’t seem to be anyone in the US selling a stand alone urine diverter, especially with how many blog posts there were on building bucket toilets for off-grid houses, etc. That has since changed (there are now a lot more options), but I will give props to the couple in England who made a business of selling their urine diverter online. I paid $45 on eBay, which seemed a little steep for a molded piece of plastic, but it was definitely quick and easy, and I’ve been happy with the product and design.
So then how to improve on the #2 part? Well, it seems like ever since human kind invited cats into their homes, the problem has been “solved.” Yes, I believe that a human litter box is the way to go. They key to this, however, is the exhaust fan. The reason a composting toilet functions well is because there is a 12v continuous exhaust fan sucking out any odor and making sure the compartment is void of all moisture. As long as this idea is incorporated, the human litter box is a great solution.
So basically, all one needs to do is build a fancy “outhouse” setup where the toilet in the Airstream would normally go. A cabinet box houses the bin that will catch the solids as well as the urine diverter and the exhaust fan. You need a deck on top of the cabinet with a toilet seat attached. That’s pretty much it.
For the deck, I wanted a solid material that is as easy as possible to clean (for obvious reasons), thus, I chose a heavy duty commercial kitchen cutting board (18″x24″). It’s an inch thick, so plenty solid, and it’s made to be easily wiped completely clean (removing bacteria, etc., in a kitchen setting). I searched a bit online and found the Winco CBXH-1824 for $30 from a commercial kitchen supplier. I used the toilet seat as a template, and then cut the hole with a reciprocating saw. I then used a router to round off the sharp edge.
For the seat, I chose a “soft close” hinge (it doesn’t slam) and found a seat with a lid that is actually molded over the edge of the seat, to form a kind of seal. I thought about making a gasket to make the seat and lid really seal, as I thought this would help mitigate odor, but it turns out that the exhaust fan really does completely eliminate odor, and leaving a little bit of an air gap around the seat (vs. sealing it completely) helps with air flow.
I was a little worried that I hadn’t left a vent stack through the roof. I didn’t want to vent through the side wall for aesthetic reasons, and I was worried that venting through the floor wouldn’t work very well. I did some poking around online, and there were a few people who had installed set ups in their Sprinter vans that included exhaust vents through the floor, so I decided to give it a try. It has worked great. No complaints with functionality, and after a year of use, any worry about excessive odor due to not venting above the nose line has been assuaged.
The vent fan box build…
The most convenient way to plumb the urine diverter in my build was to pipe into the lavatory sink drain pipe. This has the added bonus of “flushing” the toilet (anything standing in the drain pipe) when you wash your hands. I though that was pretty clever.
So I just place a trash bag in the bin (the plastic container that the kitty litter came in happens to be the perfect size), ad a little kitty litter (like, just a couple cups), and the exhaust fan takes care of the rest. With two people, every couple of weeks or so I take the deck off the toilet cabinet and remove the bag from the bin and toss it in a dumpster. We’ve been using this set up for more than a year, and I have to say I’m extremely pleased with the results. And there has never been any odor! My eight-year-old actually prefers the Airstream toilet to the ones in the house.