In the cassette I use Lidl washing tablets @ £2.50 for 36. I put in two at a time mostly, but can easily get away with one now that the weather's cooler.
I just flush with fresh water (I catch rainwater with my awning). I empty it into any toilet (even public ones at night when it's quiet), with the occasional burial' when I'm in the middle of nowhere.
There is very little smell (even when emptying) and I use the toilet all the time; not just for number twos as some people on here advocate.
I used the pink and blue stuff when I first started out, but the smell is terrible, it's expensive, it stains like hell, it's bad for the environment (and poisonous) and you can't just bury it or flush it down a toilet without potentially causing problems to both sewage treatment works and septic tanks.
Before changing to these tablets, I thought about the SOG system. However, as this method is so successful, I can't see any reason for doing so now - especially considering the OTT price of £120.00 (you could make your own for under £20.00).