I simply added an additional AN832-4D fitting and associated hardware with a rigid line out to the third bay
I don't see any reason for running a line out to the 3rd bay.
Simply terminating the return line at the fitting works just fine.
Unlike a vent line there will always be fuel in that return line.
Plumbing the return line via a selector is one option or you can simply return it to the left or right tank.
The 4plex Andair fuel selector is a fine work of art, however it is a tall stack
and a pricey addition. For the RV-10, obstructing the tunnel with such a tall stack makes running the heater hoses almost impossible. Not to mention the
nest of plumbing coming together all in the same place.
Another option and the one I choose was using an Andair fuel selector and using Vans supplied selector for the return plumbing. Clearly not as simple as the 4plex Andair set and forget but way cheaper, and much more convenient to install. An additional benefit is the option to transfer fuel from one tank to the other.
Operation simply requires that you switch both fuel selectors something the 4plex valve does with one hand motion.
I have designed my fuel system to run on 91 octane mogas and chosen a constant flow return line as a means to keep the fuel system cool and prevent
vapor lock. Doing my 3rd annual and over 300 hours of trouble free operation.
Today's mogas price $ 2.43 per Gallon