Absolutely, I figured if I've got at least a semi-decent plan when I go to qualified mates to check, it'll save their time (and my beer).

Legendary, thanks!

It'll be connected into the septic, outlet from the shed will be about where the basin is.

That was my initial thought, but that seems to take up more room than a smaller square/L shaped one.

So, building a 9x6m shed in the backyard, plan currently is to make one of the bays (so 3x6m) lined/insulated, and turn it into a spare room, with bathroom.
Originally planned…