Article updated 19.8.2026
When you’re planning the bathroom and wastewater solution for a cabin, a renovation, or an off-grid property, the real decision isn’t just which toilet to buy – it’s which wastewater system you’re committing to.
In practice there are two fundamentally different combinations:
- a dry toilet paired with greywater treatment
- a traditional water toilet paired with blackwater treatment – either a treatment plant or a sealed holding tank.
The two paths differ enormously in investment size, permitting effort, and ongoing maintenance, and in our experience the total cost difference between them can easily be a factor of ten, depending on the site.
When people hear “dry toilet,” many still picture a wooden outhouse at the bottom of the garden. That image is outdated. Today’s indoor composting toilets are built to sit inside the bathroom, right next to the shower and sink, with a real porcelain seat and none of the smell people expect.
In this article we compare two of our most popular indoor models – the Green Toilet Compact Lux and the Green Toilet Lux – against a traditional water toilet connected to a septic tank or municipal sewer, so you can choose the right solution for your home, cabin, or renovation project.
The Cost and Effort Gap
The two combinations aren’t a close call. A dry toilet with a compact greywater filter is typically a project in the range of a couple of thousand euros, installed in a day, with lighter permitting and no recurring service fees beyond an annual filter change.
A full blackwater solution – whether a treatment plant or a holding tank that needs regular emptying – is a different scale of project: more digging, more plumbing, heavier permitting, and running costs that continue for the life of the property. Depending on the site – ground conditions, distance to a water body, environmental protection zone, and the capacity needed – the total investment for a blackwater solution can easily be five to ten times higher than for a dry toilet and greywater setup
| Dry toilet + greywater treatment | Water toilet + blackwater treatment / holding tank | |
|---|---|---|
| Typical investment* | Roughly EUR 1,500–3,000 (toilet + greywater filter, installed) | Often EUR 10,000+ for a treatment plant, or a 3–12 m³ holding tank plus recurring pump-out fees |
| Ground work | Usually none or modest – ground-level installation | Typically required – digging, pipe routing |
| Permitting | Often a lighter, faster process (greywater only) | Heavier, slower process – blackwater carries more environmental/health risk |
| Electricity | A few watts for the toilet fan only | Treatment plant: yes, ongoing. Holding tank: no, but pump-out fees instead. heating of the property all year round necessary to avoid pipes to freeze |
| Ongoing maintenance | Self-service: container change for dry toilet, annual filter-mass change for grey water filter | Scheduled pump-outs or a maintenance contract |
| Water use | 0 L per use | Several liters per flush |
| Comfort today | Porcelain seat, indoor installation (e.g. Green Toilet Compact Lux, Green Toilet Lux) | Familiar porcelain fixture |
* Indicative figures based on typical projects – confirm current pricing and local permitting practice before publishing or quoting a customer.
Which Combination Fits Your Property?
If your property doesn’t have a full municipal sewer connection, a dry toilet paired with greywater treatment is almost always the lighter, faster, and cheaper route to a comfortable, compliant bathroom – and it no longer means compromising on comfort, thanks to indoor models like the Green Toilet Compact Lux or other Green Toilet options.
A full blackwater system still has its place, typically where a property already has – or is required to have – a complete sewer or treatment-plant connection regardless of toilet type. But it’s worth going in with open eyes about the investment, the permitting process, and the running costs that come with it.
When in doubt, it’s worth pricing both paths before committing to a renovation or a new build: the gap in total cost is usually the deciding factor.
Explore the Products
GeoTrap grey water purifier
GeoTrap Grey Water Filter Unit
Interested in learning more about composting toilets, grey water systems, or full off-grid sanitation solutions? At Pikkuvihreä, we’ve been helping people find smart, sustainable toilet solutions for over 30 years. Whether you’re looking for a cozy outhouse or a modern interior setup, we’re happy to help.
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Who are we?
Pikkuvihreä is a 30-year-old family business. Dry toilets, composting, and wastewater are our specialties. We serve everyone – please contact us!
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