[Neddy]

Our "new" Sprinter van came equipped with a Dometic exhaust fan mounted in the ceiling of the toilet/shower. Despite its very high noise level it is surprisingly ineffective. Unless the door is left open, the cubicle becomes very stuffy and towels hung there do not dry. The Dometic toilet was not exactly odour-free either. More ventilation was sorely needed - here is what I did.

Two 12v 80mm computer fans were installed in the door of the toilet compartment. These exhaust air to the outside. One fan would have done the job just fine, but fitting two and wiring them in series halves the power consumption and makes them completely inaudible. An "upstand" made of a few PVC plumbing offcuts was fitted to the cassette spout, screwing in place of the existing cap. This enables foul air from the cassette to be vented overboard whenever the toilet slide is opened. The power consumption of such a system is so low that it can be left on all the time. It draws just 90 milliamps - that's a mere 0.09 of an amp.
Here is the outside view. https://s16.postimg.cc/flxjdk7it/P1010038.jpg

In this photo you can see the spout "exhaust vent" that replaces the usual cassette screw cap.
https://s22.postimg.cc/3pev49x4h/P1010033.jpg
The system as installed gives a relatively modest airflow but this seems to be all that is required to achieve a fully effective result. In any case if it proved necessary, it would be very easy to increase the airflow.
Use of a single 12v fan would double the airflow and wiring the two fans in parallel instead of in series would quadruple the airflow (and the power consumption, of course).
Even when run "full bore" these fans are still inaudible from inside the vehicle.

This has proved to be a very effective solution to all our ventilation problems. We leave it on day and night all the time the van is being used. The project was quite inexpensive with the fans costing $5 each (AliExpress) and the external grilles $7 each (Smart Marine). That's just $24 all up - so long as you have got a few old PVC plumbing fittings lying around.

Comparing this to a SOG installation, this one :-
Is completely silent.
Can be left on all the time.
Ventilates the entire shower/toilet compartment.
Needs no holes drilled in the cassette.
Draws fresh air into the van through existing vents, hatches etc.
Very effective - no odour escapes even if the toilet slide is left open.
Much cheaper - $24 or so rather than $345 or more!

Neville.

[linrae]

Neville
Very interesting ,however how does that help with ventilation in the shower area??.Understand on toilet side

LIndsay .

[Derb]

Its an airflow thing Neville- You cant suck air out of a sealed container. Those Dometic extractor fans work real beaut as long as you have somewhere for the air to come from - such as a door left ajar in the other end of the bathroom. A simple fix would be a grille or vent in the door or wall at the other end of the bathroom with no fans required The fans would no doubt remove "other odours" from the area when the Dometic fan was not being used.

[Neddy]

How does that help with ventilation in the shower area? LIndsay.

Unlike Thetford toilets, Dometic models allow a flow of air between the "cassette garage" and the toilet/shower cubicle. This means that when the fans are on, air flows from the van living area to the cubicle then into the "cassette garage" and outside via the fans whether the toilet slide is open or not.
Thetford toilets need to be set up differently and are best exhausted "under floor" via a single fan mounted in the special cavity moulded into the base of the "cassette garage".

Those Dometic extractor fans work real beaut as long as you have somewhere for the air to come from - such as a door left ajar in the other end of the bathroom.

There is a 1" gap along the top of the shower door that lets in plenty of air when the Dometic ceiling fan or my exhaust fans are on. Leaving the Dometic fan screaming its head off for long enough to dry a towel would be absolutely unthinkable!

Neville.

[scubadoo]

Thank you Neville for your detailed DIY method. I'm sure it will save a few many dollars.
I will definately not be showing it to our neighbours here who just spent $600 having the "official" version installed yesterday.
Fortunately with the the judicious use of the appropriate of toilet chemicals, smellies and ventilation we have not had any issues from our C400 toilet cassette system to date.

... An "upstand" made of a few PVC plumbing offcuts was fitted to the cassette spout, screwing in place of the existing cap. This enables foul air from the cassette to be vented overboard whenever the toilet slide is opened....

For our future reference, where and how is that "upstand" terminated and is there likely to be any spillage from a full cassette on the seriously rough and winding roads we often travel?

[Neddy]

The spout terminates in a 350mm vertical stand-pipe of 35mm diameter. I suspect this is way more than is needed and I can't see any cassette contents scaling that height no matter how severe the braking or cornering. Especially since the length of 50mm diameter horizontal pouring spout would have to be filled before anything even reached the stand-pipe.

[Nut17]

Timely to revisit this subject as the price of a genuine SOG has gone through the roof. Close to $500 for a through the floor model to suit the Dometic "Saneo" toilet fitted to our new rig. Quote from Lewis Carrol below:
"The SOG II (vented through the floor) price is $456.00 plus $18.50 for
freight, $473.50 Incl. GST. please add a further $4.00 to this balance if Rural mail applies.
If you operate a second cassette then for a further $50.00; incl. GST we can supply a second cassette fitting."

I like the concept of your twin fan system Neddy, although I am having trouble diverting my thoughts away from the SOG system where the air is drawn directly through the cassette when the slide is opened. We have separate shower and toilet enclosures opening into the bedroom and shut off from the rest of the living area. Each of these does have a roof mounted extraction fan which at you have commented appear to lack efficiency when taking size and noise into consideration.
I have been given a 75 mm 12 volt computer fan that I will get Ben to 3D print a manifold to suit and mount under the floor and attach a flexible pipe to a push fit tube through the screw emptying cap using a rubber grommet for a seal.
That is the plan at this stage anyway.

[Paul-Carter]

I installed a 12v compressor fridge and it happens to be next to the bathroom. To give some air movement over the heat exchanger coils on the back I cut a hole through into the bathroom and as above wired in a computer case fan.
Result the fridge works like a trojan. Set to anything above half scale and the tomatoes freeze in the veg box and the bathroom has become a very good drying room, wet shoes placed directly in the fand flow are dry the next morning