Steve Farmer wrote:How about throwing a few flushable chunks of charcoal into the toilet every x number of flushes? Would this save the need to open the IBC and add straw etc, or would it just end in  charcoal sludge similar to the problems of using sawdust?

Charcoal floats! You might have a problem getting it to flush. I really don't know what would happen as it's not something I've considered trying. It's possible to add it to the system, but personally I wouldn't rely on it as the only carbon component. It's not the natural habitat of worms and their associated ecosystem - that's the litter layer of the soil - so I think I would be very cautious about using it in concentration. Bottom line is that I try to imitate nature as much as possible. I think it's far less likely you'll go wrong doing that.

Just to update everyone on the system ...

It's now been approved for use by my local municipality under the provisions for 'septic tank with drainage'. (To alter legislation to give it specific approval would take far too long and the council wanted to start using the system right away.) Last summer myself and a Portuguese architect oversaw the first municipal installation of the system to replace a failed septic tank. There are more in the pipeline.

The design has been open-sourced and I've now created a website for it, including full construction details, maintenance, case studies and a forum where the community of users can ask questions and discuss problems.