We have had couple of the cheaper no name chemical loo's and they worked fine but both ended up leaking yellow water if you know what I mean
We now use a Thetford and it hasnt leaked. We are on our second one...I ran over our first one. As for emptying either I am not a huge fan but couple of things that we have learnt over the years.....
1, Use proper chemicals. We tried the napisan idea and for us it didnt cut it. Proper chemicals or pods smell like roses.
2, Empty it at a designated dump point. They are set up for it and a lot nicer doing it outdoors using a hose rather than at home in the loo.
3, It has already been mentioned but only put enough water in the top flushing tank to get you by until your ready to empty the bottom, it makes it a lot easier to lift.
4, The most important one, dont forget to empty it after a trip. Ours lives behind our stoneguard on the camper and yes I did forget to empty once, and it was back when we were trialling napisan
Oh and one more......watch out for splash back when emptying