Airhead 'Composting' Toilet
A toilet was a key component of our build, since we’ll often be camping well away from amenities, and we liked the idea of a “composting” (more properly a separating) toilet.
We decided on the Airhead composting toilet over Nature’s head because we liked the ease of removal of the liquids container. We expect to be using (and emptying) the liquids container far more frequently than the solids container, so the ability to remove it without requiring removal of the solids top was key. We also liked the possibility of having both inflow and outflow air vented directly outside, rather than requiring the inflow air from the van. Others have reported that in some wind conditions the toilet vent fan can be overpowered, and venting is reversed into the van cabin. Not the end of the world, just a bit of earthy smell, but something to avoid if possible.
To save floor space we put the toilet on a sliding drawer in our passenger-side cabinet. The drawer is made from 1⁄2” Baltic Birch plywood (Kreg Jig is great!), but the anchoring screws provided by Airhead are too long, so the first order of business was cutting them down. A metal-cutting bandsaw and grinder would have been nice, but a hacksaw and Dremel worked well enough.
We offset the toilet in the drawer to make more room for the stirring handle and more leg room close to the van wall.
The Airhead comes with a vent hose, fan and fitting for the exhaust, but initially I thought the fan fitting was a bit big. I tried making a smaller fan box from PVC, but after a few test builds, decided that the Airhead fitting was better than anything I would build. The fan hub diameter is almost the size of the vent hose, so having space for air mixing on both sides of the fan is important.
I saw mention of people using a carbon filter instead of outside exhaust and a 4” hydroponics filter looks like it may be feasible. This didn’t pass the Wife Acceptance Test though, so back to outside exhaust. I built an outside vent from PVC pipe and fine-mesh hardware cloth. Rather than screwing it to the van floor, it is press-fit and glued, so it can be removed by just cutting the PVC pipe apart.
I used some standard 22” full extension drawer slides from ebay. I also added some low-friction tape on the bottom of the drawer so it could rest barely above the floor and support our weight sitting on the toilet when extended. Attaching the slides to the t-slot frame required some 80-20 1020 (1”x2” extrusion) to raise the slides high enough off the floor.
UPDATE (2018-09-08): After we decided on a 24V house battery, I chose to replace the 60mm 12V fan with a similar 60mm 24V fan. This allows the fan to run continuously, even when the 24V to 12V converters are disabled. (Originally I also planned to have 12V power only in the kitchen galley, but later found enough other uses for 12V power to include it on the passenger side as well, so we could go back to a 12V fan if needed)