My gut feeling is that it will end up drawing from one and not the other. If you keep every hose length from the tee identical and both tanks at the same elevation it may work. In any case if it didn't work all you would need to do is install a shut off valve on each tank branch so you could draw one down and then the other. Give it a try ans let us know. Best of luck. Rick.
you will end up drawing from one first then the other, then simply sucking air and not running
best to put a valve in between to switch between the two
Uhhh, I'm probably missing the point here... but what's the problem with using a single hose and disconnecting from the first tank when it runs low and connecting to the second tank? You won't have to worry about sucking air and you're less likely to have any dangerous leaking fuel lines in the boat. The more splices you have in a fuel line the more likely you are to have a leak.