Spend any time talking to full-time travellers about their van toilet and the SOG system comes up fast. It is one of the most popular caravan toilet upgrades in Australia, and for one simple reason: it deals with the single problem every onboard toilet has, which is smell. This guide explains what a SOG system is, how it works, what it costs, and whether it earns a spot in your setup for the big lap.
The short version up front: a SOG system is not a toilet. It is a small, fan-based ventilation kit that bolts onto the cassette toilet you already have, vents odours straight outside, and does away with the need for toilet chemicals. Whether that is worth it comes down to how you travel, and we will get to that.
What Is a SOG System?
A SOG system is a ventilation kit that retrofits to an existing cassette toilet. It does not replace your toilet or change how it looks; it works quietly in the background on the waste holding tank and its surrounding components. The kit is German-made and has been around for decades, which is part of why it has such a loyal following among caravanners.
The kit itself is simple: a small 12V fan, a length of hose, and an external activated charcoal filter that sits behind a vent. That vent can go through the toilet service door, through the floor, or through the roof, depending on which model you fit. SOG kits are made to suit the popular Thetford and Dometic cassette toilets, and even some permanent black water tanks, so most vans on the road can take one.
How a SOG System Actually Works
The clever part is the trigger. The fan is wired to your toilet’s blade valve, the flap you open to drop waste into the cassette. The moment you open that valve, the fan switches on. It draws air down through the bowl and into the cassette, creating a gentle suction, or negative pressure, inside the tank.
That downward airflow acts as a seal. Because air is being pulled in through the valve rather than allowed to drift out, the gases and smells simply cannot rise back up into the bowl and bathroom. The extracted air is pushed outside through the charcoal filter, which neutralises the odour before it reaches the air, so your neighbours at the next site never cop a whiff either.
Close the valve and the fan stops, but the system keeps a permanent vent open to the outside. That constant trickle of fresh air feeds oxygen into the cassette, and oxygen is what the microorganisms breaking down the waste actually need. More oxygen means faster, more complete decomposition of both waste and paper, which is exactly why you no longer need chemical additives to control the smell. The whole thing sips power too, drawing around 0.43 watts, so it is a non-issue for your battery setup.
Forget the special “biodegradable” caravan toilet paper once you have a SOG fitted. Ordinary supermarket toilet paper is recommended, because the oxygen does the breaking down, not the chemicals.
The Real Benefits On a Big Lap
It genuinely kills the smell
The obvious win is that it kills the smell, and it does so well. Owners are close to unanimous on this point, even the sceptics who fitted one expecting marketing hype. For a couple or family living in a van full-time, a genuinely odour-free toilet is not a small thing.
You can ditch the chemicals
The bigger long-term benefit is dropping chemicals altogether. Over a year on the road, the running cost of blue and green toilet additives adds up, they take up cupboard space you do not have to spare, and most of them are not kind to the environment or to the dump points you rely on. A SOG removes that cost and hassle entirely. If you want to weigh that against sticking with additives, our guide to caravan toilet chemicals covers what is worth buying if you keep using them.
Easier, less frequent emptying
There is a practical upside at the dump point as well. Because the contents break down more thoroughly, the cassette tends to empty more cleanly and needs emptying a little less often, especially since you are not adding two litres of water with every chemical dose. For free campers spending long stretches off-grid, that is a real day-to-day improvement.
The Downsides Worth Knowing
A SOG is not for everyone or every setup, so go in with eyes open.
It only suits cassette toilets
The system only works with a compatible cassette toilet. If you run a composting or gravity-style toilet, it is not relevant to you at all. If you are still deciding on a toilet type, our guide on composting versus cassette toilets is the place to start.
It is a permanent modification
Fitting one means cutting a vent through your service door, floor or roof, so it is not something you undo easily. The install itself is a straightforward DIY job for anyone reasonably handy, usually a couple of hours with no auto electrician needed, but it is still a hole in your van. Door-mounted models also need a minimum mounting depth of about 30mm, so thinner service doors need a small ply packer behind the fan.
It needs power, and the odd new filter
The active suction relies on 12V power. If your batteries are flat, the fan will not run, though the passive vent still does its job. The charcoal filter is a consumable too, needing replacement every so often at roughly $36 a time. Worth noting: some travellers report the printed instructions do not line up perfectly with the newest Dometic cassettes, so a quick look at an installation video for your exact model saves a lot of head-scratching.
SOG kits are model-specific. A Type F kit will not fit a Thetford C200, and a Dometic 3000A kit will not fit a Thetford at all. Confirm your exact toilet model before you order, or you will end up returning it.
Which SOG Type Suits Your Toilet?
Every SOG kit is matched to a particular toilet, and the “Type” letter tells you which one. Check the model number stamped on your cassette, then match it to the table below. Most retailers also run an online compatibility search tool if you are unsure.
| Your Cassette Toilet | SOG Type | Vent Options | Approx. Price |
|---|---|---|---|
| Thetford C2 / C3 / C4 | Type A | Door, roof or floor | ~$380 |
| Thetford C200 | Type B | Door, roof or floor | ~$380 |
| Thetford C220 | Type H | Door, roof or floor | ~$380 |
| Thetford C250 / C260 | Type F | Door, roof or floor | ~$380 |
| Thetford C400 / C401 / C402 | Type D | Door, roof or floor | ~$380 |
| Thetford C500 | Type G | Door or roof | ~$380 |
| Dometic CT3000 / CT4000 | Type 3000A | Door or floor | ~$380 |
| Dometic Saneo | Type 320S | Door or floor | ~$380 |
Pricing usually lands somewhere between ~$250 and ~$400 depending on the retailer, the door colour you choose, and whether a sale is on, plus the occasional ~$36 charcoal filter down the track. Caravan RV Camping, My Generator and Aussie Traveller all stock the full range across every type and vent direction.
On vent direction: the door or side-wall model is the most common and vents through your existing service hatch. Choose the floor model (the SOG II) if your service hatch opens out into your awning area, since you will not want odour venting there while you are sitting under the annexe. The floor model can run a hose up to three metres to a better outlet point.
So, Do You Actually Need One?
Here is the honest answer, split by how you actually travel.
If you free camp and live in the van full-time: a SOG is close to essential and one of the best-value upgrades you can make. The consensus among full-time lappers is overwhelmingly positive, and the smell problem it solves is the exact problem that makes people nervous about using their van toilet in the first place.
If you are sick of chemicals: that alone justifies the spend over a long trip, between the ongoing cost, the storage space, and the faff of dosing every time.
If you mostly use amenities blocks: you can probably get by on chemicals, using the van loo just for midnight wees. Even then, plenty of people fit a SOG simply to never think about toilet smell again.
For most people doing a genuine big lap, a SOG lands as one of the cheapest modifications that meaningfully improves everyday van life. If it fits your toilet and your budget, it is an easy yes.
- A SOG is a fan-based ventilation kit for cassette toilets, not a toilet itself, and it vents odours outside through a charcoal filter.
- It removes the need for toilet chemicals, lets you use ordinary toilet paper, and draws almost no power.
- Kits are model-specific, so match the Type to your exact Thetford or Dometic cassette before buying. Budget roughly $250 to $400.
- For full-time travellers and free campers, it is one of the best-value upgrades going. For occasional users relying on amenities blocks, it is optional.
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