A composting toilet in an RV keeps liquids and solids in separate containers, dries the solids with a small 12 V fan that vents outside, and sends nothing to the black tank. You empty the liquids bottle every day or two and the solids bin every few weeks.
Composting Toilets in an RV: How They Work and What Changes for the Black Tank
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At a glance
- How it works: urine is diverted at the seat, solids sit in a vented bin, and the toilet uses no water and no black tank connection.
- How often you empty: the liquids bottle every day or two on most models (Air Head's large tank 2 to 4 days), the solids bin after roughly 25 to 80 uses.
- Not finished compost: two of the makers say the contents still need six to twelve months of composting after they leave the toilet.
On this page (7)
Our picks
- Nature's Head composting toilet: 20 x 19 x 21 in; vent it through a sidewall or the roof
- OGO Origin compact composting toilet: 16 x 15 in footprint; push-button electric agitator
- Organic coco coir bricks, 10 pack: bulking material for Nature's Head, Air Head and OGO bins; Separett needs none
How does a composting toilet work?
Unlike the flush toilet your rig came with, it keeps urine and solids apart, and that is what stops the sewage smell. Nature's Head says separating urine from solids is the key to odorless operation.
Each maker separates differently. OGO's Origin diverts urine with a trap door and mixes the solids bin with a push-button electric agitator. Air Head collects liquids in a forward tank and agitates the solids in the large tank behind it.
What happens in the bin is drying, not composting. Nature's Head says the coco coir or peat moss and the fan dry the solids in the short term, while turning them into fertilizer depends on time and temperature. Separett says the waste is not composted when you empty the bucket.
Bulking material: makers disagree
Nature's Head, Air Head and OGO expect coco coir or peat moss in the solids bin, replaced at each emptying. Separett says no cranking or additives are needed, and that bulking material fills the container faster and can draw fine dust into the fan. Follow the manual for your model.
How often do I have to empty it?
Plan around the liquids bottle, because it fills long before the solids bin.
- Nature's Head: solids bin holds roughly 60 to 80 solid uses; urine bottle holds 2.2 gallons. Empty the solids when the agitator handle gets hard to turn.
- Air Head: its FAQ says the solids tank averages 80 uses, about a month for two people, with the small liquids tank emptied every 1 to 2 days for two people and the large one every 2 to 4 days.
- OGO Origin: 2.4 gallon urine bottle, every 2 to 3 days for one person or 1 to 2 days for two; solids bin about 25 to 30 uses.
- Separett Tiny: with two users, the 2 gallon urine container every other day and the 2.65 gallon solids container once a week.
Nature's Head says urine diluted with at least 50 percent water can go on mature trees or plants, and solids ideally go to a compost pile, or in a bag or buried while traveling. Air Head says bagged solids can go in a trash receptacle away from home, after checking with local authorities. OGO notes that full composting takes 6 to 12 months after the waste leaves the bin.
State disposal rules are written for houses and vary: Indiana sends the residue to an approved landfill, while Massachusetts allows burial at least six inches deep where the local Board of Health approves. Check where you are parked.
Tip: Nature's Head says not to leave urine sitting in the bottle for long, because it smells worse over time, and for full-time users to wait 6 to 8 hours after the last use before emptying the solids.
Do RV composting toilets smell?
Not while the fan runs nonstop and vents outside. Nature's Head tells RV, van and skoolie owners to vent through a sidewall or the roof, not through the floor of a moving vehicle. Separett says never to switch the Tiny's 20.5 CFM fan off with waste inside, or odors follow and flies may lay eggs in the solids.
Power draw is small:
- Nature's Head: under 1.8 amp-hours in 24 hours.
- Air Head: about 0.06 amps, roughly 1.44 amp-hours a day.
- Separett Tiny: 0.04 kWh per 24 hours, at 12 V and 1.6 W.
- OGO: no fan draw published; it specifies a 12 V, 10 A supply with a 10 amp inline fuse.
For the vent hose, OGO's 3-foot reinforced hose fits over 1-1/4 inch PVC, and the Separett Tiny allows up to 16 feet of pipe with two 90 degree bends.
What happens to my black tank?
The tank that used to take every flush stops filling, since OGO says its toilets need no water, chemicals, plumbing or black tanks. No maker says whether to drain, cap or keep it, so that depends on what else drains into it.
OGO's optional floor riser plate can be installed over an old black tank flange to seal the old holes and give a level mounting surface; OGO says to check under the floor before drilling. Air Head's Tejo model ships without a urine tank so the liquids can be plumbed straight into an existing holding tank.
Separett says urine separated at the seat is not black water, since it never meets fecal matter, and can go to a grey water tank in a camper. Nature's Head sells urine diverter models that route liquids out through the floor to an external tank. Air Head notes that US regulations prohibit discharging untreated urine into waterways.
Will one fit where the old toilet was?
Most are shorter and narrower than a residential flush toilet, and all of them bolt to the floor. Pulling the old unit out is the first job either way.
| Model | Size (W x D x H) | Weight |
|---|---|---|
| Nature's Head standard | 20 x 19 x 21 in | 23 lb |
| Nature's Head Weekender | 18 x 18 x 16.75 in | 19 lb |
| OGO Origin | 16 x 15 x 18.375 in | Not published |
| Separett Tiny | 15.7 x 19.6 x 18.5 in | 18.7 lb |
Figures from the makers' pages: Nature's Head, OGO and Separett. Air Head publishes drawings only and gives the complete unit as approximately 25 to 30 lb. Only Separett prints a seat height, 17.3 to 17.7 inches, so measure what you have before ordering. OGO also recommends a 2 inch gap behind the toilet for the vent hose and power jack.
What about incinerating toilets?
These burn the waste instead of drying it, and they need far more power than a composting toilet. Incinolet's manual calls for a dedicated 20 amp circuit with a 20 amp receptacle and a vent to the outside. Cinderella Travel burns propane or diesel, with a 12 V supply for the electronics, and vents out through the roof. Installation is a job for a qualified technician: Cinderella's Freedom GAS NA manual requires an authorized specialist for the gas, the electrics and the leak and flame tests.
Common questions
What are the drawbacks of a composting toilet?
You handle the waste yourself, often. Nature's Head also notes that nothing composts below about 55°F, so in cold weather the bin can freeze solid and the agitator will not turn.
Do RV composting toilets smell?
Where you notice the smell tells you which fault you have. Air Head says odor inside the living space points to a ventilation problem, so check the hose, the fan and the exterior outlet; a strong smell at the exterior vent instead means there is too much moisture in the solids tank.
Is a composting toilet better than a black tank in an RV?
It trades one chore for another. You can camp much longer between dump stations and stop using fresh water to flush, but you take on frequent small emptyings, and the solids still need composting after they leave the bin.
Can you have an incinerating toilet in an RV?
Only some models are meant for it. Cinderella's Travel unit is sold for motorhomes and caravans and Incinolet's mobile and marine version is its Model WB, but Cinderella's Freedom GAS NA manual states the appliance must not be installed in a recreational vehicle.