DIY Composting Toilet for RV

Gordon goes over designing, building and using this very functional composting toilet for an RV or cabin.

It can be built for a few dollars and works as well or better than commercial alternatives.

RV composting toilet

Thanks very much to Gordon and Sue for providing a practical and inexpensive composting toilet design and a wealth of practical information on how to use it successfully.


DIY Composting Toilet Made From Olive Barrel

This is the composting toilet that Gordon and Sue have used for several years in their small RV. The design is based on years of experience with commercial composting toilets and works very well.

The nice thing is that it can be made for just a few dollars.

How Its Built

The composting chamber is an unmodified plastic olive barrel that was donated by a neighbor. It came with a twist off lid that was simply removed and not used. It has an about 12 inch opening with a maximum diameter of about 16 inches. The height is about 24 inches. The barrel is sturdy enough not to require any support -- this requires a wall thickness of about 1/8 inch or a bit more. More on finding a good barrel below.

The toilet seat was salvaged from an old RV toilet. The toilet seat needs to be a rather tight air seal.


diy composting toilet



diy composting toilet for RV

It may be difficult to locate the exact type of barrel that Gordon used, but here is some advice from Gordon on what makes a good choice:

Gordon's barrel is about 18 US gallons. It is a recycled polypropylene olive barrel, and if you can locate one of these, that would be great, but there are alternatives around.

If you Google or search ebay something like "15 gallon plastic barrel", quite a few come up. There may well be some local sources of lightly used barrels from Craigslist or local merchants.

The wall thickness should be 1/8 inch or greater and a good barrel will likely weigh about 7 lbs.


The space on each side of the barrel holds a dozen spare TP rolls, some diatomaceous earth for occasionally controlling fruit-flies & no-see-ums, and a stirring stick made from 3/16" drill rod.

As a composting carbon source we use a mix of sphagnum 'peat' moss, wood shavings and wood saw-dust. It's stored in the wooden box to the rear of the toilet.

The muffin fan, which is installed at the start of the black duct exhausts air from the composting chamber out the exhaust vent on the side of the camper -- this pulls fresh air into the screened air intake for the toilet. The muffin fan is a 12 volt DC fan that only draws about 100 milliamps and uses only 1.3 watts. The 3 inch flexible black duct, and the fittings at both ends are typical RV black-water tank dumping parts. They had become surplus years earlier with the compost toilet conversion of an earlier small camper trailer.


RV with composting toilet


Stir Stick

From time to time, some air must be stirred into the mixture to keep the decomposition aerobic.

composting toilet stir stick toilet

Gordon on using the stir stick:

If the mass becomes too moist, or if there is a considerable mass of material, or if one has been driving some rough, pounding roads, then the mass tends to become 'packed'. The decomposition processing still continues, but favours anaerobic bacteria rather than the desired aerobic bacteria. The anaerobic process is slower, and tends to be stinky.

Many commercial units have a method to tumble the barrel to break up the mass and continue aerobic processing. This seems like a great feature, but when the bearings fail, mid-vacation, a 1000 miles from home, and sticking one's finger in the dyke is not the answer, perhaps simplicity is better - first hand experience, says Sue!

This tumbling feature is not implemented in our ultra simple 'Olive' barrel design, and from experience, I don't recommend pulling the barrel and trying to roll it around :) !!

However, we have found that using a stirring stick for perhaps 2 or 3 minutes to dig into the mass, and lift it up (perhaps 2") from the bottom of the barrel, for 3 or 4 times, breaks it up sufficiently to allow aerobic processing to continue and provides the 'visual' to ascertain whether:

- it is too dry (and needs some water), or

- too moist (and needs additional 'carbon'), or

- flies might be becoming an issue (and needing a quick powder spray (~ teaspoon to tablespoon) of diatomaceous earth - the latter being perhaps once every other year!

Stirring is typically required:

- about once a week during continuous use by two people, or

- once a month or so, during occasional or weekend use.


Gordon and Sue have been using composting toilets in RVs and cabins for more than 20 years...

We ended up purchasing a used truck top camper - a fairly short one. The disadvantage of the short length was no toilet (but far too many gismos!).

However, we'd already decided to go with a composting toilet - so no problem. Nearly 20 years ago we put a Sun-Mar NE in the loft of our super-tiny 175 yr old log cabin in the bush with a 5w solar panel to power the toilet's muffin fan and the one tiny lamp in the cabin. Has worked flawlessly - well almost - lesson, if too dry, do not moisten with swamp water - culturing mosquitos and black flies is not recommended!

Since then, we've ripped out black-water systems from two very small RV camper trailers & replaced then with the Sun-Mar SpaceSaver (sailboat & square footprint versions).

No the small Sun-Mars don't fully compost things (about half way), but digging a bushel basket sized hole in the back-yard at season end is no big deal .

In the case of the truck camper, Sun-Mar toilets aren't inexpensive, so we decided to roll our own. We highly recommend it!!

The toilet seat was salvaged from an old RV toilet, a neighbor provided the olive barrel, and the muffin fan, switches etc are from my junk bin. Total cost - nil !!

The toilet seat needs to be a rather tight air seal.

The space on each side of the barrel holds a dozen spare TP rolls, some diatomaceous earth for occasionally controlling fruit-flies & no-see-ums, and a stirring stick made from 3/16" drill rod.

As a composting carbon source we use a mix of sphagnum 'peat' moss, wood shavings and wood saw-dust. It's stored in the wooden box to the rear of the toilet.


Using the Composting Toilet

Some points that Gordon makes on using composting toilets:

- They are not for everyone. You have to be a bit open minded and a bit flexible.

- They are appropriate for certain needs, but certainly not all needs. Perfect for those living in their own dwelling/camper, but not for a commercial wedding factory dealing with hundreds of people per day, or for a very major rest-stop on a major multi-lane highway - with bus loads of people.

- there is a bit of a learning curve, (no big deal). Think Goldilocks - not too wet, not too dry; not too little carbon or too much).

- there are limits that require some respect - mostly common sense. True composting is a large hot aerobic mass - not possible in a small barrel.

- no cigarette butts, no tampons, no toxic chemicals.

- there is a bit of management required (but nothing excessive)

- Add a half cup of peat/sawdust per pee, & add a full cup for a poo (it's not rocket science).

- Next year, finish the mass in a hole out in a corner of the garden.

- The barrel does not evaporate enough for constant two person use, so:

- If in a restaurant, use their facilities (no big deal).
- If male, try to make 1st pee of the day in a bottle & empty bottle every 3 or 4 days in an appropriate place (again, no big deal);

- If only used on weekends, it will become too dry. So, add a cup of water (not swamp water) from time to time.

- If the camper is in use and the barrel has been used, (unless it is quite cold) use the muffin fan (at 12V and 100 ma, power is trivial & essentially noiseless).


There are great, but unforeseen advantages.

With no black-water tanks to leak or spill, add a PV module and:

- Campsite management will invite you to camp on pristine beaches or adjacent to water falls and rapids.

- Boon-docking is much more pleasurable.

- You have a longer camping season with no need to worry about frozen/leaking black-water tanks and lines. It may be too cool to compost, but composting can wait until warmer weather.


Some of my questions answered by Gordon:

Question: If using the composting toiler while RVing, will it last for (say) a couple week trip without filling up? Or, how long would you expect it to last if two people were using it as their only toilet?

It depends upon usage:

In the case of the cabin and little camper trailers usage (family of 3 or 4, primarily summer weekend use, plus a 2 to 3 week vacation trip) we would empty and clean in the early spring (i.e.: once per year).

Sue & I took the truck camper (with olive barrel) to Newfoundland two summers ago. It was the ideal rig for that (very sparse accommodations, wild, rugged, & mountainous). That province actually encourages boon-docking! We were about 6 weeks on the road.
Normally, if boondocking, we try to get a motel every 4th night or so to properly shower (and, motel perhaps weekly, if in gov/commercial campsites). Thinking back, we only had 4 nights in motels over the 6 weeks (I said facilities were sparse).

We do tend to have one meal a day in a restaurant (lessening the load - so to speak).

In any event, the barrel ended up about 1/3 full, (probably could have gone another 2 or 3 weeks) - being somewhat full, I did empty it that fall and buried the matter - so to speak. Usually, I've been lazy, and do that come springtime.

Question: The toilet accommodates solids and liquids? No smell with the muffin fan vent and good seal? Does the muffin fan run all the time?

This comes back to 'not for everyone' & 'management'! Smell largely arises due to anaerobic decaying animal matter.
Thus one needs to avoid a too moist situation:

- A once a day male pee bottle seems to do the trick (an all day long beer habit just won't do it!)

- If on an extended holiday, try to reduce or avoid red meat consumption -- - it's usually not difficult to eat more fresh vegetables in summertime.

- The muffin fan provides a slight negative pressure - enough to vent almost all odours. That said, try to keep your pillow some distance from the toilet (but to be honest, in our log cabin, it's no more than 3 feet away).

- the seal at the toilet seat is not a big issue, it's more a matter of keeping fruit flies & no-see-ums from getting into the barrel to propagate, and keeping them from getting back into the camper afterwards :)

- the (passive) air intake on top of the seat cover and 'dryer vent' exhaust on the exterior wall both have fine window screening to prevent critters (if you do get critters, simply sprinkle a little diatomaceous earth);

- the muffin fan is attached to the seat top, sucking fumes out of the barrel, and pushing them up the flex duct to the outside. The fans primary function is to evaporate excessive moisture to maintain an aerobic environment (which has very little smell! ) Louvres on the outside of the dryer vent prevent rain entry into the ducting.

Added comment from Gordon 9/11/14:

I forgot to mention that with several/numerous days of rain, humidity being high, the little muffin fan just can't evaporate moisture quick enough. Thus the action tends to go anaerobic - ie: not an issue inside, but somewhat stinky outside. This might be a bit of an issue if neighbouring campsites are overly tight (ie: <~ 10-15 ft). Once the weather cleared, things got back to normal. I doubt that this will be an issue for you in Montana, but it could be an issue in the humid south-east U.S. in summertime, or west coast most anytime.

Commercial Options

There are some commercial options for compact composting toilets:

Sun-Mar Spacesaver ...

Nature's Head compact composting toilet...



Humanure Handbook...


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