Hi Julie.
We have a thetford toilet in our van , a swivel as well all that means is you can spin it round if you like to make it more comfy when using . As for chemicals well on the discharge spout on the cassette there is a built in measuring scale, i add about 60ml of kem blue straight into the holding tank . As our toilet has a electric flush it has its own tank of clean water which i add around 20ml of pink rince , so when you flush loo its nice and pink . All the chemicals do is to keep any nasty smells away and i must say they do work . The chemicals can be bought from your local Caravan shop or online.
Hope this has been of help .
Dougie.............