1 roll of 25 specialised composting loo container liners.  
Fully compostable for your compost bin.
Use these if you aren't keen on cleaning out your solids container, but it's just one more thing for nature to deal with. Plus they can sweat and smell themselves.
We line the bottom of our solids container with sawdust and that works perfect when it comes to emptying out; keeps things dry and fall-out friendly ;)