I use plain water. I cannot see any reason to add anything. The previous owner of my previous caravan had used pink in the flush tank & it was full of black bits. It took several fills of plain water to get rid of them.
For the cassette tank I use cheap bio wash liquid. Lidl Formil. Hand wash my clothes in it as well so one bottle does both.
As well is two words!
How does a sage know everything about everything? or does he? or does he just think he does?
Remember, if you buy something you bought it, not brought it.
We used to use Thetford pink and found that it caused the black bits. We switched to Elsan pink and no more black bits. However, I only use about a tablespoonful per full tank so quite a weak solution.
The purpose of putting anything in the flush water is to help disinfect the toilet bowl and to help lubricate the seal in the cassette. It is not mandatory and you can put in whatever you like or nothing as long as you are happy with the outcome. Some people use plain water, some use a few drops of zoflora or other similar disinfectant, it is really a matter of personal choice.
We've been using Zoflora to get rid of the black bits after a neighbour gave us some unused Thetford pink when they got rid of their van. We may just stick with it for a bit longer.
Dave.
------------- Give a man a fish and he will eat for a day,
Teach a man to fish and you can get rid of him for a whole weekend.
Without double checking I seem to recall that the 'Pink' is mainly detergent, perfume, colourant and thickening agent. I've never really seen the benefit of it, especially as its something else to buy and carry about.
------------- 'A sure cure for sea-sickness is to sit under a tree'
My old caravan had black bits in the flush water, the previous owner had used pink in the top tank.
In my new one I use non-biological laundry liquid in the top tank. No black bit and a nice clean toilet. For me an advantage of this is the top tank will not freeze unless it gets very very cold and as we caravan all year it helps
------------- We camped for years. In 2019 we bought an Elddis Avante 454. We like it as it is short (6.9m) and fits in our driveway and has a fixed bed.
We had 127 nights away in the caravan in 2023.