My Promaster Van Build: Rear Entry, Hidden Bath/Shower, and a Few Other Unusual Details

Page 12: DIY “Composting Toilet” and Spreadsheet Of Total Build Costs

 

I’ve saved the best for last: the potty. Not having a black water tank and a flush toilet has been one of the biggest improvements over the Chinook. I had issues with a leak in its tank, and even after I fixed that by replacing it, it invariably began to make its presence known after a couple of days. Stephanie is a super-sniffer, and it impinged somewhat on the enjoyment of being in the outdoors.

There are of course many options to black water tanks, including various portable units, but they all have to be emptied, which is not exactly fun and does require a proper toilet or outhouse to dump into. Since we tend to be off in the boonies a lot, that wasn’t very appealing.

My musings on the subject lead me to composting toilets, such as this one by Nature’s Head. The key thing to know is that modern composting toilets work well precisely because they separate the pee from the poo, via a urine diverter that directs the pee into a separate storage vessel that is easily emptied, and safely/legally so in many places. The poo is kept in an air tight container where it’s mixed with a drying material such as peat moss or coir (coconut husk fiber) and uses a small fan to constantly create a flow of air to enhance the drying.

The key thing is the drying, as poo is some 90% water and the bacterial action (smell) continues as long as there is sufficient moisture. Once it’s dry, there’s essentially zero smell.

I was all set to buy a Nature’s Head, which costs close to $1000 with shipping, but then I read about Gary’s home-built “composting” potty at his buildagreenrv site. Frankly, it’s more accurate to call it (and my version) “a urine-diverting poo-desiccating storage device” as realistically that’s what it is. One can in theory compost the poo by putting it into the ground at home after a trip, and leaving it for a year or more to make it usable as compost in vegetable gardens, but it hardly seems worth the effort. It’s just a lot more pragmatic to legally dispose of the plastic bag in the garbage.

So I decided to build my own too, and see if it would pass muster with Stephanie. It’s going to be easier to comprehend if I show it in reverse order, starting with lifting the lid, which has a rubber gasket to make an air-tight seal when it’s closed. The white plastic thing in the front is the urine diverter, which I had to buy from a little outfit in Great Britain ($45). Obviously it requires sitting only, which is not a bad idea in a small van or RV anyway.

Lifting the hinged top of the box reveals that the urine diverter directs the pee into a standard one-gallon bottle (preferably with a flip lid so as to not lose it) via a small funnel. The funnel was initially just a temporary solution, but it works fine and is there to stay. The second bottle next to it is of course there to swap out if needed. I underestimated our pee output on one of our first trips and found an inch of pee on the bottom of the box. Since I glued it with urethane and gave it several coats of clear polyurethane, there was no leakage.

Another option I’m still considering is to have a flexible hose from the diverter to the sink drain and into the gray water tank.  This is actually ok, as urine is aseptic unless one has a bladder infection, and can be safely/legally  disposed of in the woods, just like taking a very long pee. But the bottles are probbaly here to stay and work fine.

The 5 gallon bucket has a standard kitchen garbage bag, and gets primed with a few scoops of coir, which works even better than peat moss. After making a deposit, a scoop or so of additional coir is added from the container that rides right next to the potty. It’s really kind of like a litter box, but works better and is air tight.

Here’s the box without the containers. I routed out recesses for the bucket and bottles, and glued pieces of pink insulation so as to firmly hold them in place. At the upper right side of the back, there is an inlet vent, juts a hole with a fine screen on it. On the lower far corner there is an outlet vent, a PVC pipe with a tiny PC fan on it.

The 40 mm miniature fan is essentially noiseless, and draws a very small amount of current when it’s turned on by the switch, at the time of first use. The pipe it sits on goes out the bottom of the box and through a hole in the van, where there’s also a fine screen to keep bugs out.

Somewhat ironically, we’ve hardly ever used it (for poo), as Stephanie has joined me in using alternatives such as outhouses, campgrounds, etc. and even the woods, where appropriate, with a trowel to dig a hole and cover it up. She used to really insist on a toilet, but now that’s changed. So I’m even more glad I didn’t buy an expensive toilet system.

But we did use it on one of our first trips, and it worked better than expected. Absolutely no smell, and it was so much nicer to just tie up the bag and toss it in the garbage than to have to drive the Chinook out to our sewage treatment facility to dump and rinse out the tank after coming home from a trip.

The gray water drain hose is stored behind the potty.

And the fresh water hose has a nook between the potty and the galley cabinet. The wood toilet seat was glued and screwed to the top of the box lid.

 

Conversion costs spreadsheet:

I tallied up my parts and materials costs on a spreadsheet. I might have missed something, so I added a contingency. I did buy a few tools, such as the Kreg jig and a Rivnut set, but I’m quite likely to use them again in the future. These items were all bought in 2018, the majority on Amazon, so the prices may have changed since then.

In retrospect, I might have been able to save a few bucks here and there, but in the balance, I have almost no regrets. There are some minor things that I would have done differently, besides of course a lot of head scratching and researching. I purposely did not track my hours spent on the conversion, as undoubtedly they are more than I would like to admit. But it’s been a very fun and satisfying project, and the new challenges were something I was looking for. Yes, I could probably do a second one in half the time, but that’s not the point.

I’ve already had a couple of folks ask me if I would build a similar van for them. Sorry; but I’d rather be out in the desert in my van.

Return to page 1 for the index of pages

 

Here’s links to some to our van and trips so far:

My New Future Campsite Classic: 2107 Ram Promaster

Oregon Cascades: Our First Trip in the Promaster

A Seven-day 1700 Mile Loop of the Mountains and Deserts of Eastern Oregon

Derrick Caves: Probing the Promaster’s Off-road Capabilities

Van-Tripping 4300 Miles through Arizona, Nevada and California

 

 

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