We've just had a week at the NPWS Coochin Creek camping ground in Beerwah SF on the Sunny Coast.
They have long drops (although new flush dunnies are just about finished 
) that you are supposed to drop a cup of sawdust into after use.
They were fine with regards to smell, although Mrs said that the women's ran out of sawdust on arvo of our 2nd day & by the 3rd day they were all a bit off 
Ranger visited that day, replenished the sawdust supply & they were fine after that. Don't know if he did anything "downstairs" to make the smell go away 
Also don't know why a cup of sawdust should do much / anything to kill the stink
My
guess is that they are a form of composting toilet, the theory behind them is if you keep the number two's dry, there isn't anywhere near the smell, kind of like a dog turd on the grass after a day or so and it has dried out and there is no smell.
It's when you mix ones and twos that you get sewerage and the real pong.
I have seen setups where people use sawdust to help dry out the two's but they generally separate out the ones so they don't come into contact with the two's to start with. Maybe they have some kind of filter that lets the liquids through but not the solids and then the sawdust helps to dry out the number two's.
