How does one make a sewer treatment plant in a bucket

This is a pet project of mine. the idea is that treatment of sewer on a small scale which then can be scaled up. If a sewer is small and cheap to make then problems of health can be addressed worldwide.
Population is expanding and the infrastructure is not or is slow to take up the slack.


The system needs to service a family of five and be the size of a bucket that's the brief.

So lets all think about the solution.