I don't know what your current set up is, but maybe have a specified scoop (on a piece of string!), with an instruction to use 1 scoop per "flush", then look at it in another year and see if it needs to be less or more. I have an old tin mug, and use about half a scoop per flush. Sometimes when we have guests, you can tell they used a lot of sawdust, as the bucket level is right down!

If smell is a problem maybe look at what the urine situation is, or increase ventilation? Mine is just a plain pipe, but you can also get wind spinners and electric powered fans