I think my boats drawing more fuel from one then the other. Id rather run one tank up river then one back down
you should ALWAYS have a valve on each tank. if you're not running a valve you are flirting with disaster if you ever have a fuel leak. you'll have no way to shut off the fuel.
im a big fan of keep it simple. 90* ball valves on the tanks, to a fuel/water separator. you'll run both tanks into it, and use one output. run that to the fuel pump, after the fuel pump run a small micron inline fuel filter to catch the small bits, and then into the carb. try to keep bends to a minimum etc. every bend, every 90* fitting, etc can lower fuel pressure.
but safety first. you MUST have a valve on each tank to shut off the fuel.
if you want to run off one tank, just turn off the other side and it'll suck from the open tank. run both, open em both up. just realize that it'll suck from the easiest tank that it can pull from so it wont be 100% even.