No such thing as a van composting toilet. A better term is a crap bucket. I didn't even want to spend the money on a diverter so use a £1.50 funnel from screwfix into a petrol container, poo bucket is £1 from screwfix, add in a bit of wood, etc total cost is negligible. I found trying to push the air out with a fan didn't work very well so I put the (92mm) fan on the outside of the van and pull the air through the toilet, the natures head etc only have a 40mm fan which I can't believe does anything as it's trying to push the air through a coiled tube. I don't use any sawdust, there's no smell and I throw it away every 3 or 4 days. I imagine there would be a smell if I left it much longer with no sawdust.