Start with the name, because the name is the problem. What the industry sells as an RV composting toilet does not compost anything. It is a urine-diverting dry toilet: liquids go to a bottle, solids go to a bin with a dry bulking medium, and a small fan pulls air through to keep the solids dry and the smell outside.
Decomposition begins in the bin. It does not finish there. Waste pulled out of an actively used vehicle toilet after a week has not become sanitised compost and cannot be treated as though it has — manufacturers themselves say the contents should be composted properly before any further use, which is not a thing you can do from a parking space in Utah. Treat what comes out as human waste, because that is what it is.
That correction matters, because most of the enthusiasm for these units rests on the idea that you are converting a waste problem into garden soil. You are not. You are making a different trade, and the trade is genuinely good for some people and genuinely bad for others.
What you are actually trading
A black tank concentrates the unpleasantness: nothing to think about for four to seven days, then twenty minutes with a sewer hose at a dump station.
A dry toilet distributes it: thirty seconds of handling a bottle of urine every one to three days, plus a solids bin emptied every three to six weeks for two people. It is never a big job and it is never finished.
Some people find the second arrangement obviously better. Some find it obviously worse. Neither reaction is wrong, and no amount of specification comparison will change which one you have. What the specification comparison can tell you is what else changes.
| Black tank | Urine-diverting dry toilet | |
|---|---|---|
| Capital cost | Fitted as standard | $250 for basic portables; $900–$1,050 for Nature’s Head or OGO-class units; $1,100+ for cartridge systems |
| Install | Already there | Half a day: mount, run a vent through the wall or floor, wire a 12V feed. Removing the old toilet and capping the black plumbing adds time |
| Water use | ~0.3 gal per flush; roughly 1.75 gal per person per day | None |
| Emptying: liquids | With the tank | Urine bottle every 1–3 days for two people. This is the real schedule driver |
| Emptying: solids | Every 4–7 days at a dump station | Every 3–6 weeks for two people, bagged and binned where permitted |
| Consumables | Tank treatment chemicals, $50–100/yr | Coir or peat bulking medium, ~$10 a brick; bin liners |
| Dependencies | Water pressure, dump station access | Continuous 12V fan, roughly 1–3W. Fan failure means odour within a day |
| Odour when working | Managed, occasionally not | Genuinely low — urine separation plus airflow is what does it |
| Odour when not working | Bad | Bad, and closer to you |
| Winter | Freeze risk in tank, valves and dump line | No freeze risk in the unit itself |
| Weight and space | Tank, water, plumbing | Lighter overall, but the unit itself has a larger footprint than a standard RV toilet and often needs a taller seat height |
| Resale | Neutral | Divides buyers sharply. Keep the original toilet and the capped plumbing intact |
The urine bottle sets your life, not the solids bin
Every enthusiast review leads with the solids interval, because three to six weeks sounds transformative next to a black tank’s four to seven days.
The solids interval is not your schedule. The urine bottle is. Typical bottles hold around two gallons, and two adults fill one every one to three days. That means finding somewhere acceptable to empty it every one to three days — a public restroom, a dump station, an RV toilet, a sewer connection. In a town, trivial. Nine days into a stretch of dispersed camping on public land where the rules on liquid waste disposal are exactly as strict as they are for solids, considerably less trivial.
This is the fact that determines whether a dry toilet actually extends your off-grid range, and it is systematically underplayed. It does extend it — but by less than the solids interval implies, and the extension is in a currency (short frequent trips) rather than the one people expect (long uninterrupted stays).
What it reliably does extend is your tank runtime for everything else. Removing toilet flushes takes roughly 1.75 gallons per person per day off your fresh draw and empties the black tank column of the sizing arithmetic entirely. On rigs where black was the binding constraint, that is a real gain — though on most rigs it wasn’t, because grey is almost always the tank that ends the trip, and a dry toilet does nothing for grey.
The fan is a system dependency and people forget it
Odour control in these units is not magic and it is not the coir. It is two things: keeping urine away from solids, and moving air continuously through the solids chamber and out of the vehicle.
That fan runs permanently. It is a small load — typically 1 to 3 watts, so 25 to 70 Wh a day — which is trivial against any real house battery and non-trivial against nothing at all if you are storing the rig with the batteries disconnected. Fan failure, a blocked vent or a vent routed somewhere with backpressure produces smell inside the vehicle within about twenty-four hours.
Carry a spare fan. They are inexpensive, they are the single point of failure in the design, and replacing one in the field is a ten-minute job that you very much want to be able to do.
What the install actually involves
The units are marketed as drop-in replacements. They are not, quite, and three physical constraints catch people out.
The vent. The fan needs a path outside, which means a hole through the wall or the floor, sealed properly, positioned so the exhaust does not sit under a window or vent into a wheel well. Long runs and tight bends reduce airflow enough to matter — keep the duct short, and use smooth pipe rather than corrugated flexible hose if you have the choice.
The footprint and seat height. Most of these units are wider and taller than the RV toilet they replace. In a wet bath measured to the inch, a dry toilet can make the shower unusable, and the higher seat is a genuine problem for shorter users. Measure before ordering, including the door swing and the space needed to lift the top section clear when emptying the solids bin.
The mounting. The unit must be bolted down hard enough that it does not shift when the bin is agitated or removed in transit, and the floor under an old RV toilet is not always sound — it is one of the more common places to find soft subfloor from a slow leak. Budget for the possibility that the two-hour job becomes a floor repair.
The plumbing you leave behind. Cap the black tank inlet properly and leave the tank vented. An abandoned, sealed black tank with residue in it is a smell you will spend a summer chasing.
Disposal is the legal problem, not the toilet
The toilet is rarely what regulators care about. Where the contents go is.
Depositing human waste on the ground is prohibited across federal land management agencies — Forest Service sanitation rules, wildlife refuge disposal rules and BLM regulations all cover it, and “it’s biodegradable” is not a defence anywhere. Bagged solids in a dumpster is what most manufacturers suggest and what most people do, but campgrounds, municipalities and some states have their own positions on that, and they are not uniform.
For fixed installations — cabins, tiny houses, permanent structures — the picture is more regulated still. Composting toilets are broadly permitted somewhere in the region of twenty states without special conditions, and conditionally permitted in most of the rest, frequently with requirements that the unit be certified to NSF/ANSI 41, that a permit be obtained from the state or county health department, and that an approved greywater disposal system exist separately. Several states allow them only where a sewer connection or approved septic system is also present, which defeats a good deal of the point.
None of that is stable enough to summarise here in a way that will still be true when you read it. The state-by-state reference on septic, greywater and water rights covers the current position, and for anything permanent you verify with the county health department before you buy the unit, not after.
Five years of costs, honestly
| Black tank | Dry toilet | |
|---|---|---|
| Purchase and install | $0 | $950 unit + $0–300 install parts |
| Consumables, 5 years | $250–500 chemicals | $200–350 coir and liners |
| Water saved | — | ~1.75 gal/person/day, ~$0 direct but real range value |
| Dump fees | $10–25 per visit, more visits | Fewer dedicated dump trips, more restroom stops |
| Repairs | Valve seals, sensors, occasional macerator | Fan (~$25), latches, seals |
| Five-year total | $250–700 | $1,150–1,600 |
The dry toilet does not pay for itself in cash. It pays for itself in capacity, in not having to handle a sewer hose, and in eliminating one of the more expensive freeze-failure modes on the rig. Whether those are worth a thousand dollars is a preference, not a calculation — the same way most of the recurring line items in a proper full-time cost breakdown turn out to be preferences with prices attached.
Who should switch
Switch if: you have no black tank and no room for one — van conversions, teardrops, small trailers, skoolie builds where the plumbing was never installed. You are full-time and boondock more than you hook up. Your rig winters in a cold climate and the black tank has already cost you money. Your black tank is genuinely the constraint on your stays.
Don’t switch if: you camp mainly with hookups, in which case you are adding a manual task to replace an automatic one. You are squeamish about direct handling — be honest, because this is the main reason units end up on the second-hand market. You share the rig with people who will not follow the sit-down discipline urine diversion requires. Your grey tank is the binding constraint, because this changes nothing about that.
Consider the middle option: a cassette toilet. Flushes with a small water charge, has a removable 5-gallon holding tank you carry to a toilet or dump point, no black tank, no fan, no bulking medium, no handling of solids, and roughly a fifth of the purchase price. It is emptied every two to four days for two people. Nobody markets it as a lifestyle upgrade, which is probably why it is under-considered.
FAQ
Do composting toilets actually smell? Not when the urine separation and the fan are both working — that combination is why they don’t smell like a black tank. When the fan fails, the vent blocks, or urine gets into the solids bin, they smell quickly and inside the vehicle.
Where do I empty the solids? Bagged and sealed into a permitted waste receptacle in most cases. Never on the ground, never in a storm drain, never at your campsite. Rules vary by campground, municipality and state, so check locally rather than assuming a dumpster is universally acceptable.
How often does the urine bottle need emptying? Every one to three days for two adults with a typical two-gallon bottle. This is the interval that governs your planning, not the three-to-six-week solids interval quoted in marketing.
Can I use the compost on a garden? Not from an RV unit. What comes out has not composted long enough to be sanitised, and pathogen die-off in properly managed composting takes months under controlled conditions. Treat the contents as human waste.
Do I need a permit? For a vehicle, generally not — but you are bound by disposal rules wherever you happen to be. For a fixed structure, frequently yes, and several states also require NSF/ANSI 41 certification and a separately approved greywater system.
Does removing the black tank hurt resale value? It narrows your buyer pool. Keep the original toilet, cap the black plumbing rather than cutting it, and keep the parts — a reversible conversion is worth substantially more than an irreversible one.
Does a dry toilet mean I need less water treatment? No. Flush water and drinking water are separate problems, and what treatment you need depends on your source regardless of what your toilet does.