I think we need to be reminded about what the chemicals are for.
Traditionally, two chemicals were used - one for the flush and one for the holding tank. Why? Because the one in the holding tank was both a strong skin irritant and didn't smell very nice, so the flush chemical was "kinder" and perfumed to counteract the harsh smell below.
Recently the formulation of the holding tank chemical has been changed to eliminate formaldehyde, which is a particularly nasty concoction. Now the more ecologically kind chemicals can be used both top and bottom - in the flush and the holding tank.
So, what do the chemicals do? First of all, they kill bacteria in the sewage which helps to stop gas build-up and foul smells. Second, they help break down solid matter and paper, to make emptying the tank easier. Thirdly, they kill algae in the flush tank, which can block pipes and pumps if left unchecked. Fourthly, they help lubricate the bowl, so "things" don't stick.
Which fluid you use is a personal preference and also depends on what kind of camping you do. You can decide not to use any, as vwalan suggests, but I wouldn't go down that route.
------------- * You never know where you're going 'til you get there...
i ralley a lot with the c & c club and live in fields. twice ive made the mistake of not forgetting to emoty the loo wot a nasty niff. and it took a good while to get rid of the smell .now always rinse mine 3 or 4 times till the water is clear. and if im going home i put a good dollop of the blue stuff in . always seems to work.
Still on about the ,Black bits lol,but what it is ,when the pink stuff is added to the flush tank i have them ,but when i only add water i dont , i think the reason for this is that ,when only filling with water a build up if mold in the form of a black sludge is alowed to acumulate in the tank ,when yousing the pink stuff ,it washes it out ,/so the black stuff every one mentions is flusht out ,and helps deoderize the toilet,so i think its doing it job .only my opinion ,could be wrong ,
------------- May the roof of your camper
never fall in ,and the couple inside ,never fall out,
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.
Topic: Smelly cassette toilet
I just wish you hadn't said "lubricate the bowl"...... 
