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Cassette Lining


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I have a new to me motorhome with a Thetford CT 4000 cassette toilet. It was making a rattling/thumping noise whern emptied. On inspection, it is lined with a relatively rough light brown coating ( no it's not! ). It appears to be some sort of ceramic but it is breaking up and I can see the blue plastic underneath it. Is this disastrous or can it be lived with?
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brayncc - 2020-07-26 6:15 PM I handled it, it crumbled much too easily.


I wouldn't handle it any more it's a normal by product. I found after I stopped using blue an switched to bio liquid it cleared away eventually

(Formil bio from lidil)

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brayncc - 2020-07-26 6:15 PM


The van is a 2013 East Neuk Fifer. To be honest, it doesn't feel like ceramic when I handled it, it crumbled much too easily. Limescale was not on my radar but is a thought provoking alternative!


As has been advised above, the light brown lining is ‘scale’ that will build up over time unless a toilet cassette’s interior is kept ckean.


There is plenty of on-line advice on cleaning methods




Thetford markets a specific product




or you could use a strongish citric acid solution.


This 2008 forum discussion may also be of interest




In fact, although Thetford produces a C4000 range of toilets, your Fifer probably has a DOMETIC CT4000 toilet with a ceramic inlay bowl (image of cassette attached below) - but the Thetford cleaning advice will apply equally well to Dometic toilets.




It’s perhaps also worth adding that - if there’s a rattling/thumping noise from inside the cassette when it is being emptied, something internal may have become detached. When emptying a toilet cassette, some people shake the cassette violently and internal components can fall off their mounting or become damaged. If a cassette becomes badly damaged, Dometic (and Thetford) offers a cassette 'renew kit’ that includes a new seat and can be less expensive than buying the cassette alone (sample advert here).




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