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Venting a toilet cassette: why, what, when and how

Bette Cosgrove and Miriam Richardson


 The new regulations, brought in by the previous government and supported by the current one require all black waste tanks to be vented, including those tanks that are part of a cassette-type toilet. 

But: The NZMCA has declined to participate in the new green warrant self-containment system until this absurdity has been removed, and there are promises that a change is being prepared— as it is enshrined in the law, this is a slow process, that might eventuate by the end of 2024.

For those who do not wish to freedom camp there is no need to address this issue at all. The laws and regulations only apply to freedom camping.


The actual regulations:

20 Ventilation system specifications

In order to meet the requirement for self-containment relating to a ventilation system in regulation 13(h) [“a ventilation system that removes odours from the motor vehicle and minimises the extent to which foul air and gases can enter the motor vehicle”], a motor vehicle must have a ventilation system that—

(a) ensures unpleasant or unhealthy odours and foul air easily escape to the exterior of the motor vehicle; and

(b) ventilates wastewater storage tanks directly to the exterior of the motor vehicle to ensure that foul air and noxious gases do not accumulate inside the tanks; and

(c) includes vent outlets for wastewater storage tanks that—

(i) are installed at a height that safely prevents wastewater leakage; and

(ii) terminate outside the motor vehicle and away from doors, windows, or openings; and

(iii) are fitted with a means to prevent the entry of birds and vermin into the system; and

(d) includes pipes connecting sanitary appliances and sanitary fixtures to wastewater storage tanks that are fitted with a means of limiting the escape of foul air and noxious gases from the tanks to the interior of the motor vehicle, such as a water trap.

Plumbers, Gasfitters, and Drainlayers (Self-Contained Vehicles) Regulations 2023 Part 2, Inspection and certification of self-contained motor vehicles Read regs


Anyone wanting a new, green warrant right now has to address this issue, including those developing a camping vehicle, or whose blue warrant has expired. (Note: There are other issues to be addressed for a green warrant, it is not just cassette venting, see What you need for a green warrant for freedom camping)

There is still time, for those whose blue self-containment warrant was obtained before 6 June 2024. They can continue to freedom camp until 7 June 2025, when the transition period ends and the law requires (only) a green warrant.

If you can wait. it is possible this requirement and the associated expenses will be removed.


It is a changing playing field at present. There are three methods available at present:

  • Purpose-designed SOG system.

  • Ventilate the cassette locker (some cassettes).

  • DIY ventilate the cassette.

  • Problems with doing it:

  • A hole is needed in the vehicle envelope, with dangers around warranty, water ingress, rust and vermin.

  • The vent outlet must be “away from doors, windows, or openings”, but “away from” is not defined.

  • Removing smell from the inside to the outside might not be in favour with nearby campers.

  • With vague requirements, some inspectors might approve what others do not, which might lead to problems downstream for re-certifiying or selling. 

SOG system

Those with Dometic or Thetford cassette toilets can install the SOG system ( This is a commercial product specifically designed to ventilate these particular cassette toilets. The regulations make the vent outlet position a potential issue, but this system will not otherwise pose any problems to certifiers, nor for resale. The main limitation of this system is cost.

Ventilate the cassette locker

A May ’24 email from NZSC, Plumbers Gasfitters and Drainlayers Board (PGDB), reported on Facebook (, has stated that if the cassette has an auto-vent into a sealed locker, the locker can be ventilated instead of the cassette itself. This change, PGDB write, “would meet the functional requirement of Regulation 20(b) despite not strictly meeting the wording of that regulation.” This interpretation is not yet reflected in the PGDB documentation, and some inspectors may refuse to certify vehicles with the cassette ventilated in this way. 

Ventilate the cassette

Consider the location of the vent, the size of the pipe, preventing back flow or leakage, disconnecting for emptying without spills. PGDB have recommended but do not require a particular pipe size for ventilation.

You can create a DIY vent pipe and add this to the cap (picture 1) or air vent inlet area of the cassette (there’s some people selling DIY kits already), or to the cassette body (see picture 2 & 3). Ensure you manage non-return, prevent overflows or spills and meet the height requirements of the pipes etc. 

Picture 1: BedVanz venting solution. The pipe rises above the level of the highest water level in the loo, and then goes down through the floor. When emptying, the hose can be detached and a cap (pictured) put in its place so that it can be carried without spilling. ©2024 BedVanz Ltd,

Picture 2 & 3: Irrigation plumbing used to provide venting from a cassette.These tiny tubes have flexibility and make less impact on the vehicle envelope, and could be easily removed and the holes repaired if/when regulations change. ©2024 NZ Lifestyle Camping Ltd

For advice and support, join this Facebook group:  Self Containment New Zealand Conversion and Advisement

Freedom camping & self-containment

2 Where are we at with self-containment and freedom camping?

2 Who can freedom camp from now until 7 June 2025?

4 Getting your camping vehicle certified

8 Am I freedom camping?

8 What you need for a green warrant for freedom camping

10 Planning a toilet for the freedom camping green warrant?

12 Venting a toilet cassette: why, what, when and how

14 Keeping up with the self-containment changes

16 Composting and coddiwompling ︎

The laws and regulations only apply to freedom camping.

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