If you're almost home and have "Both" selected, and one tank runs dry, what do you end up with in the fuel line?  I believe mostly air.  Late in the trip (traffic pattern?) where trouble shooting time is at a premium.  Use L or R.  Not B.

I don’t think so: connect two tanks (one full with water and one empty) to gravity feed Into Y connection.  Than suck on the end and try to breathe. Let me know how it works :)
Buly