I'm going to say this and I want you to know that this is not an attack, just an awareness and a warning so bad things don't happen.
Drawing off both tanks simultaneously is silly. Absolutely no reason to do so.
That being said, you know what that valve was for?
It's called an anti siphon valve. The reason it's there is to prevent the draining of the tank in the chance that you have a fuel leak below the fuel level in the tank. This could be anything from a cracked fuel fitting, bad hose, failed fuel pump, anything. Those check valves in my opinion, need to be in there. What I would recommend is replacing both tank siphon valves with new brass ones (don't waste your time with the aluminum) and buy two, full port ball valves and install them on the tee. Run both valves open if you want, but throttle the "fast" tank. This way, when you are running low on fuel, you can ensure getting back to the beach. You just shut the empty tanks valve.
Do you have dual level senders?
There was a burned boat just the other day that someone had video of, that right there is reason enough to do it right (not to mention legal).
You nearly blew up the engine running lean if the previous information isn't enough.
Be safe and have fun, you can do both at the same time. Trust me.
GT
