There are fantastic (and free!) resources for planning one, e.g., this and this. NB being NB, government regulations aren't super helpful for doing things using common sense and physics, rather than by-the-book and grid-based. The current regulations stipulate that a "non-conventional" sewage system must be designed by an engineer and installed by a licensed person (I have still not been able to find one of the latter). Since our kinda-neighbours on the Kingston peninsula are building a legitimate off-grid Earth Ship, complete with all the permits, we could basically follow in their footsteps (= creep up on their FB page and find & hire all the people that did the work for them).
Once I talked to the environmental engineer that designed their greywater system, I got discouraged. He suggested we use a septic tank and a pump, both things that I was trying to avoid - greywater that sits for > 24 h will become fetid, and relying on pumps may be a big mistake. Apart from pushing us to use system components I didn't want to use, the exercise would be quite expensive (and that's before the installation costs!).
Josh provided the voice of reason, as usual. Current plan? Install a composting toilet and go ahead with a septic tank/field "conventional" installation. However, plumbing design will also have to include stub outs - allowing us to incorporate a greywater system down the road, once regulation is more flexible and we have a better feel for what would work for us.
Of all our water will end up being used for irrigation. The initial treatments will likely include things like mycelium filtering and reed bed treatment. The outflow water will have to be lab-tested a few times under different scenarios to ensure proper filtration is taking place.
In the meantime, here's a picture of the system I thought up. I wonder, once we have our system up and running, how naive and silly will this look to me? Can only guess at how many details and important bits I didn't even think of at this point :-)
