The build

SC, does this treatment plant thingy need emptying? Like a septic tank?

If treated correctly it doesn't necessarily need empting. But it can be. I think we probably will annually. Just to keep things in good order.

The effluent might be good for the garden or compost heap but I expect there a so many rules and regs that say you can't,

After using a composting toilet for nearly 12 months! We really don’t need any of the contents of the treatment plant. I have 4 daleks full. And it will stay in them for another couple of years before it get used in the garden anywhere.