Will Strivens

Beginners Guide to Caravan Cassette Toilets and Chemicals

Thursday, 2 January 2020  |  Will Strivens

There is nothing worse than a smelly toilet! And while looking after our household toilet takes very little special care, a caravan or motorhome toilet needs a little more thought in order to avoid bad smells or damage to the toilet system, not forgetting the effect the chemicals could have on waste treatment plants, such as septic tanks if not properly applied.

Cassette toilet overview

There are are two main parts of a caravan cassette toilet. 

  1. The Cassette (the actual toilet bowl inside the van)         2.  The Waste holding tank (where toilet waste is collected, ready to be emptied) 


What are the chemicals for and what do they do?

There are three main types of chemical used with cassette toilets. 

Holding tank chemicals

These additives tend to be liquid and come in 1-2 litre bottles but can range down to more compact 375ml bottles for the weight conscious. Thetford also do a handy crystalised version that comes in pre-measured sachets. All you have to do is simply pop a sachet into to your tank along with 2-3 litres of water and you're done. 

It's worth noting that some additives are very harsh and can damage the seals of your cassette toilet. A good tip is to add the chemical via the waste outlet tube while the tank is not inside the van. This will prevent both damage to the seals and mitigate the risk of staining soft furnishings inside your van.

Make sure you use the specially designed toilet paper that is made to breakdown easy in your cassette toilet. This will prevent blockages and make it easy to empty the tank. 

There are environmentally conscious and green versions of these products on the market which are septic tank safe because, unlike the standard products on the market, they don't kill the bacteria that are found inside septic tanks. The bacteria found in septic tanks are crucial in order for them to function and break down waste. 


These additives are the most important in terms of a function as they are responsible for reducing gas build up, preventing nasty smells and  breaking down the solids and tissue which would otherwise cause blockages.

Because of their job is to liquify solids, a cassette toilet is much more likely to become blocked if these chemicals are not used.

Even when using the right chemicals and correct doses, your holding tank can become blocked due to excessive use of toilet paper! Care must be taken when un-blocking it as there is a delicate float mechanism inside which is used to show how full the tank is.

Resist the temptation to fill with water and vigorously shake the tank as this is a common way of damaging the float! Instead, use a gentle swirling technique to try and dislodge any blockage.

Most modern waste holding tanks have a large removable section on the top which can be removed, making it very easy to inspect for damage and remove stubborn blockages. If you have an older tank it may be harder to resolve a blockage, please refer to your toilets manual for advice. 


At the end of the season or when your are not planning on using you van for a prolonged period it is recommended to clean the tank with a tank cleaner. Thetford suggest using a tank cleaner 2-3 times a year in order to prolong the tanks life, keep it looking like new and importantly to keep it smelling fresh!


Flush chemicals

In recent years flush chemicals such as Thetford aqua rinse have developed to leave a pleasant smell and satisfying shine to the cassette bowl. However, these chemicals are not as important as the ones used in the waste holding tank as their only function is to leave the bowl clean and smelling fresh after a flush. 


Toilet bowl chemicals

Specific bleaches and spays used for keeping the toilet bowl clean and hygienic have to be plastic safe in order to avoid damage to the toilets plastics, pipes and seals. Thetford have released a couple of products that are specifically designed for cassette toilets and they are pictured below.


Top Tips!

  • Always remove your tank from your van and add the chemicals outside so you don't spill and stain your van!


  • Be careful where you place your lid when emptying the waste holding tank... you don't want to lose it down the drain too!


  • Use olive oil as a seal lubricant and keep your seals in tip top condition... this will help prevent any leakage!


  • Always use easily degradable toilet pager and use it sparingly! 

Below is a handy diagram from Thetford which helps to give a visual representation of what goes where!

Image sourced from: https://www.thetford-europe.com/gb/which-thetford-toilet-care-products-do-i-need

Thetford, (2020), 201811015_Thetford_Afbeeldingen_Website_EN [ONLINE]. Available at: https://www.thetford-europe.com/gb/which-thetford-toilet-care-products-do-i-need [Accessed 6 January 2020].