We've a couple of composting toilets here, one in the house, one outside. Both were built into existing spaces so no chance for chambers etc. We seperate urine and solids, compost the solids in a series of bins, and put the pee on our compost heaps. Both require emptying, the house one more often as the tanks are smaller - weekly - and the outside one less often - monthly. The inside one needs a vent (which it will get soon), and the outside one is well ventilated enough to not need one. The preformed plastic separators are easy to fit and work well.
Here's the outside one -
and a couple of others that we built at our last place - both treebog type designs with a large chamber below
and a twin chamber design, that we planted willow around and which is now completely concealed. Here it is without -
With the chambered treebog type toilet, the chamber is about 1m x 1m x 1m, and has straw lined walls formed with chicken wire. Ideally you have 2 chambers, so you use one for a year or two, then swap to the other, and wait until the first has composted down before using the compost. In practice the 2 chamber one has never filled up or needed emptying yet. It doesn't have a separator, but willow planted immediately around it takes up any moisture. The growth rate is phenomenal.
In all the loos I pictured we just put in a little sawdust with each use, and so far this has kept odour at bay. The problem is always with the pee, especially if its tanked for any reason. Useful as it is, a lot of designs simply head it off to a soakaway pit to avoid the problem.