thats because the salts and ammonia is getting leached out in the compost pile. if just left in the bucket to compost, the salt will just sit in there basically pickiling your sawdust . once its added to the compost pile it gets diluted and leached which allows the right bacteria and worms to go and do there jobs. some salt can be tolerated but that much just sitting in a pail won't do much but stink to high heaven!
Michael Cox wrote:Having done this for years - using a sawdust bucket as a urinal - I can say with confidence that concerns about salt build up are unjustified. Start with a few inches of sawdust in the bottom. Top up a handful at a time with sawdust as you use it, so that all urine damp sawdust is covered with fresh. This supresses all smells. As the bucket fills up you can empty it into a normal compost heap. It will get hot within a few days and be dark, rich soil in a few weeks. We haven't been using this recently, but when we do we love the benefits it brings to the compost.
This is covered in "The Humanure Handbook".
A few observations from our use:
Sawdust - especially from slightly green wood - works, better than shavings. They are more absorbent. Pine shavings, such as those used for animal bedding tend to be almost waterproof, and they don't settle as densely in the bucket.
Empty the bucket when it is about 2/3rds full. It is lighter, easier etc...
You can put a few sheets of newspaper in the bottom. The bucket will be a bit easier to clean.
If you get a smell you are doing something wrong. Add more sawdust.