Composting Toilet Build Notes

Composting toilet parts list

template routered plywood kit

molded funnel holder and split clamp bucket attachment

centrifugal fan and speed controller

vent tubing and bulkhead adapters

One sheet of ½” plywood

fan speed controller: search on eBay for “3~35V 12V 24V PWM DC Motor Speed Controller Adjustable Switch LED”. If it’s about $6-$7, that’s the right one

Fan: I’m using “12V 40mm Blower Fan 4020 40mmx20mm” from eBay


3 ea. 3/8 NPT x ½” barb fitting

24” long ½” i.d. fiber reinforced nylon tubing

3 band clamps
and then whatever it takes at the drain end to get a small plastic valve on there, and maybe a T pointing vertical with a bit of tubing on it to act as a site gauge.

ventilation system:

centrifugal fan and speed controller

vent tubing ( 1 ¼” shop vac. hose)

bulkhead adapters: 2 ea. 1 ¼” x 2” hose adapters. Cut off the 2” female extension part of the hose adapters, creating a 1 ¼” flange adapter to attach to the toilet box on one end, and the floor of the van on the other.

Toilet Seat. I’m using the Glacier Bay Elongated Soft (cushioned) seat from Home Depot.

Garbage compactor bags from Walmart

Pine shavings from Tractor Supply (or any pet supply)

Composting Toilet Notes:

Check the thickness of the plywood you use and adjust the dimension of the end boards of the main toilet box and the lid. In other words, the main width of the lower box section is 14.375”. If the front and back panels are .5” wide, then the right panel would be 13.375 to fit perfectly inside of the front and back panels.

However, if the wood you use is less than .5” thick, for example Home Depot’s Sande Ply which is 1/32” less than a half inch, then increase the width of the right panel accordingly, which would be 13 7/16”.

A full sheet of ½” plywood (or two ½ sheets) will be enough for the project with a bit left over in case you make a mistake cutting out a part or two.

Pin and Glue
Assemble parts that fit tightly with Tightbond2 or equivalent wood glue. The angled parts that make up the dirt bin/wheel well cutout would be far to complicated to make perfectly fit cuts. Cut per the design, there will be edges that fit tightly, but not the entire width of the board like wood glue needs. In these cases, I used expanding polyurethane glue (Gorilla Glue for example).

To hold parts together I used a pin gun, but one could use wire brads nailed in with a small hammer.

I carded Lightweight Spackle all over the visible parts of wood surfaces to be painted (to fill the grain and fill imperfections where wood panels didn’t get glued on perfect) and after it was dry lightly sanded with 220 grit. I used a latex (water cleanup) primer with a small roller on all the parts, and after it was dry I rolled the inside of the main box and the lid with white enamel. The brown outside of the lid (I was thinking frequent dirty hands touching it) I painted with rattle can enamel in Chestnut Brown. As of this writing I have not decided what color to paint the lower section, though I’m leaning towards flat black so as to make it somewhat low key, but it will show dirt and maybe harder to wash. I’ve also thought about tracing a vector image of a trout or something on masking tape and doing something artistic. For now I left it in white primer.

Pin the Top to the Lower Box
Three 1/4-20 round head screws hold the box “Top” to the lower box section. They pass through 1” square pieces of wood at the top of the inside of the walls of the lower box. It had been my intention to put T-nuts at the bottom of the 1” square wood so the screws would screw in, but it turned out that merely using them as pins is sufficient. One could instead install ¼” round dowel in the 1” wood and have the Top board set on them. I may do that down the road.

If using wood dowel, I thought that ¼” might be a bit small. Sometimes we get to rockin’ and rollin’, and if something impacted the Top part of the toilet, ¼” seems like it might shear. It’s up to you. Just some ideas.

Another thought is if using ¼” screws like I am, nylon screws might be better than rusting steel.

Toilet Seat
I am using the Glacier Bay Elongated Soft Toilet Seat from Home Depot. Why not have the comfort of home?

Drain Tube and Tank
I used 24” long ½” i.d. fiber reinforced tubing for the drain tube. You’ll find it in the hardware store where rolls of vinyl tubing are.

If you use the 3 gallon tank from Plastic Mart, note they offer it in two thicknesses:



5/16″ – 3/8″

Make sure to have them put an inlet hole on the centerline of the top, 8 1/2” from the aft end. Have them put a drain hole at that end, at the bottom. Your choice if it points down or aft. Mine is pointing aft.

I am using 3/8” NPT to ½” barb adapter fittings for the inlet and the outlet. Plastic-mart may only give you ½” holes, so you may choose to use 1/2”NPT to ½” barb, or you may choose to use a 1/2”-3/8” adapter and then 3/8” NPT to Barb. I recommend keeping everything plastic because of the caustic nature of our fluid.

You will need a tank breather hole. On my homemade tank I drilled a 5/32” hole near the top aft corner and that seems sufficient. You may deal with tank relief as you may best see fit.

For the drain I am using a plastic ½” barb ball valve for the outlet of the tank, except that it actually fits the next size up tubing, 5/8”, so there’s an adapter involved. It is my plan to install a T fitting between the outlet of the tank and the valve, pointing vertically upwards, with a tube attached, to function as a sight gauge for how much fluid is in the tank. As of this writing I am still looking for a small plastic ball valve that will actually fit in ½” tubing. Currently I am using a ½” to 5/8” adapter where I want the T to go.

My molded fiberglass tank has molded in hanger bolts. An idea for the Plastic-mart tank is to make a hanger plate that the tank straps to. The hanger plate might be a piece of flat aluminum long and wide enough to give good support to the tank, maybe equal to the top dimension of the tank, with a couple of bolts stuck up through it to bolt it into the van floor. The tank would steel strap perhaps, or perhaps cargo strap to the carry plate. Now that I’m writing it, I really like the cargo strap idea. Cut the strap length to fit, but that gives super easy tank removal ability.

Anyway, those are just some ideas. Share with us what you end up doing.


Fan speed controller: search on eBay for “3~35V 12V 24V PWM DC Motor Speed Controller Adjustable Switch LED”. If it’s about $6-$7, that’s the right one

Fan: I’m using “12V 40mm Blower Fan 4020 40mmx20mm” from eBay

Mount the fan and controller on a 4” long piece of 1 ½” angle aluminum. Use the thin wall stuff from the hardware store. Cut a rectangular opening in the angle aluminum for the fan’s outlet. Drill a hole for the speed controller’s adjustment shaft. Mount the fan and controller with double stick tape. Cut a rectangular opening in the toilet big enough to expose the fan outlet and speed controller knob and screw the angle aluminum to the inside wall of the toilet.

An idea for the ventilation exhaust hose is 1 ¼” shop vac hose. Use two 1 ¼” x 2” vacuum hose adapters (they’re about $6). Cut the 2” tube part off of the adapter, leaving the 1 ¼” end and a flat disk to screw to the side of the toilet box and to the van floor.

Attaching the toilet in the van:
An obvious idea is to bolt it in, and I may do that, but the floor in this area is not flat, so I put a strip of ½” plywood over where the pee tank hangs, next to it’s bolts sticking through the floor, as a shim for the back side, and the bit of indoor/outdoor carpeting I use in the back fits under the front edge just far enough to give it ok front support, and I am currently using a cargo strap to the van’s wall to basically strap the toilet vertical it keep it from moving around. It doesn’t actually tilt up and contact the wall, but it holds it nicely in a vertical position and it doesn’t seem to want to move around. I like the nearly instant ability to release the toilet if I need to, but if I put artwork on the front of the toilet, I might bolt it down to the floor anyway so the strap doesn’t cover the artwork.

Seat Cushion

Find a cushion for the top of the toilet so that it is a comfy seat. I have had Dan Futon from eBay make me custom sized foam cushions before. He might be just the ticket, but any good cushion or pillow from the thrift store should be fine.

Using the toilet for #2

I am currently using pine shavings from Tractor Supply, and the bags I’m using are the trash compacting bags from Walmart (no scent!). If it should be that in practice there is smell that the bags can’t stop, then the price of mylar bucket toilet bags might be worth it since the intent is to use one bag for a week until it’s filled up, rather than pulling it out after every use. The previous way I had used the bucket toilet required it to be dumped every day which made the mylar bags too expensive.

Prime the bucket with a good layer of wood shavings at the bottom so there’s a fair distance between the first deposit and the bottom of the bag.

Completely cover each deposit with wood shavings.

Using the toilet for #1

Prime the pee tank with some vinegar, and use a spray bottle with vinegar to spray down the funnel after each use.

The funnel I’m using appears to be widely available, although for the record I got mine at O’reilly Auto Parts, and it seems to be one of their nationally available products. They are about $5, so don’t be afraid to change it out every now and then, and maybe even keep a spare on hand for when the first one gets beyond the pale. It is a key reason for the quick change funnel feature I designed. Easy to pull and wash, or replace.

Draining the tank is done either by backing up to some natural space where it’s ok to spread some nitrogen, or attaching a short length of tubing to the valve and direct it into another container so you can carry it to a nearby dump place (like a fault or flush toilet). A collapsible blue water tote might be an idea to keep in the van for full tank draining ability. Blue to hide the appearance of what you’ll be carrying, collapsible for minimum storage size.

I do not intend to drive with a full pee tank. It should take a week to fill it, so if stationary for that long, I would drain it before driving and sloshing 30 some pounds of pee around back there. If I’m not stationary that long, I make it habit to empty every chance I get, same as I used to with pee bottles.

Men’s Use:
I find that I can kneel on the seat/lid placed on the floor next to the toilet for a quick #1. When I’m in full activity mode, I tend to have a lot of tools around my waist. With pee bottles I’m used to a quick kneel down in the back, unzip, and done in a minute, and not have to hassle with dropping my pants and all it’s accoutrements. By kneeling on the lid I find I’m just at the right height to hit the funnel. If that doesn’t work for you, then you might just maintain one pee bottle (Nalgene are the best) for the quick pees, and dump it down the funnel when you get around to it. I’m actually keeping a bottle on hand still just in case the kneeling at the toilet gets to be an issue.

Women’s Use:

Scoot forward a bit for #1 and watch your aim.