Whoa!

 

You guys think way too complicated.

 

Why not a simple wee pump to pump the aux into one of the wings.  Assuming you have a simple way to fill the aux (and vent it), this saves an expensive weird valve arrangement.  Let's see, a right-left makes an aux, a right-right makes a right,a left-off makes a left,  two lefts make a ? and two offs make quiet.  With the pump there is no necessity to also plumb in another return line.  Finally, think of the weight you will save - especially in POH pages alone.  You might even add an automatic system with a simple float valve to keep the R or L wing full until the aux was empty.

 

Trying to have three direct sources to the engine is overkill....

 

Hmmmmm, the aux needs a sump check also.  Hmmmm, the aux needs a fuel gauge too.  Welcome to the world of header tanks.