'SOG' DIY project.
Thetford Cassette Ventilation Project 

A German company called SOG make a small ventilation attachment to fit on to the Thetford toilet cassettes to remove any smells/odours from the cassette to the outside of the vehicle. Whilst the toilet/shower has been fitted with an extract fan which switches off when the Thetford toilet hatch/shutter is opened, there was a tendency for smell/odours to Ďescapeí from the cassette in to the toilet/shower, and due to the chemical additives added to the cassette, these smells/odours tended to Ďhangí on to any visitors Ė not nice. To avoid this problem, a negative pressure needed to be established in the cassette which is achieved by adding an extract fan directly on to the cassette and venting these 'fumes' to the out side of the vehicle. Additional benefits of the cassette ventilation is that there is no longer a need to use chemical additives which only 'mask' the cassette content smells.

This project basically consisted of a few snaplock connectors for the ventilation hose, suitable plastic fittings to fit on to the cassette to enable the fitting of the snaplock's on to the cassette, hose and the use of a cheap computer fan.

Thetford cassette with hole cut ready for new connection.

Two photos. LH showing the connections ready to fix to the cassette with quick release blanking cap. RH. showing the hose connections (I didn't use the bottom plastic one in the end) Photos are at different scales.

Unfortunately the cassette is made from a polythene based material, and as such nothing sticks to it very well, however with a good application of contact adhesive and some clamps, it has held together.

Above two photos showing new cassette connection in place and cassette in 'working' position. Top showing the ventilation hose fitted, and bottom with sealing/blanking cap in position for use when carrying the cassette.

Above photo showing the basic fan and filter housings. Below, same again but with a bit of finishing. When not in use, the filter housing is designed to be easily lifted off.

Below, fan housing showing fan inside.

Below, fan housing fitted into the back of the rear door, next photo down showing inside of back door with door panel fitted and ready to accept the filter housing on to the fan unit.

Back door? I didn't want to cut any more holes in the side of the van, so with a little bit of thought I came up with the idea of venting the cassette behind the rear number plate which I remounted on some wedges to allow a sufficient air gap. 

Photo below show the wedges used behind the number plate. 


Next photo shows the ventilation hole behind the number plate with plenty of Waxoyl. 


The third photo shows how well the fan vent is disguised.    

Below, finished cassette ventilation unit with connection hose fitted

The fan only runs when the toilet/shower light is on. To stop smells/odours from outside, the air is drawn through some cooker hood filter media which is heavily impregnated with charcoal.

The main reason why the above project was instigated, was that we could quite often smell the cassette contents in the van, usually when moving. After the fitting of the cassette ventilation system there were no smells at all when the van was stationary, however we still occasionally found we had smells in the van when moving. Obviously there is pressure build ups behind the van when traveling, so the first thought was that the smells were coming through poor rear door seals, especially as the smell was usually greater when the front windows were open. We tried various methods of tightening the rear doors without any noticeable difference.

Thinking how the cassette was constructed, and how it was emptied, I then realised there was a yellow button (B) you pressed to allow air in to the cassette so the contends evacuated easily. It was then, whilst examining the cassette to see if anything was stuck in the yellow button valve to keep it open I realised there was a second air valve (A) which is opened automatically when the cassette was engaged in to its housing.

On realisation that this extra vent has been the source of the smells, it was a simple job of sealing the offending vent! Since I was in France at the time, I simply taped over the vent with heavy duty tape.

Whilst not every one wants to get involved with their own SOG diy project, I can now supply them from my online shop, click here for more info



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