You really don't want to have the valve combining the tanks open except for when needed. Think about it. If you have contamonation in one tank and both engines have fuel coming in from that tank, you are liable to kill both. it's best practices to have the engines isolated to their individual tanks.
As to them drawing evenly, won't happen unless by just dumb lick. There are too many variables involved in the equation. Fuel line length, vent pressure differences, etc.
There will be one item you will want to change, that being the lingth of the genset pickup. Kohler's recommendation and the one FW foloweed is to have apickup tube for the genset configured to the half mark for the genset. It's a real pain. I changed out my tube so the genset cak use the second half of the starboard tank. We frequently run the tanks beloe half and usually on the way home, the genset would just stop.
I'd rather manage my fuel rather than have only half a starboard tank dictated to for genset use.
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Jvalich
http://www.badcock.com'04 FW 288 Vista "Mental Floss"