Avion Black & Grey Tank

My Avion had no tanks or plumbing or fixtures when i got it. THis allowed me to make my own gray water tank, and then use an Electra-magic toilet from Thetford for the black waste. It really does work well, even with my family of 6! They are a bit pricey, but not having to buy a separate black tank is nice, and I can use it in the sub freezing weather by just placing the initial charge of fluid with windshield washer fluid instead of water for flushing, and of course the formaldehyde based toilet chemical. If you were to remove your existing black tank and plumbing, you could then replace the floor of the bathroom with a flat floor that would then allow your rear overhang to be flush with the rest of the TC, then plumb the remaining below the floor of the Freightliner to what ever tanks you would like, and use what ever toilet you would like. Since you are talking desert camping mostly, you could sandwich some 2" rigid foam insulation between the floor of the TC and the bed of the truck. With a permanent mount you are rather restricted by the current black water tank, as it sits up in the TC bathroom, and drops down below th floor too, and is rather small to begin with, AND it is your grey water for the shower too, which is not a great design. Time to separate them both, and fix it so the top flange that fails on these tanks like 69 Avion had, doesn't happen to you.

Hope this helps!

Garry in the frozen north of Alaska