Jim, Air and fuel flow will do a path of least resistance. If you 't' the line the flow will go toward the easier tank. If you run separate vents it can't do that.

<... shouldn't "T" them Jim, rather bring them both out side-by-side ...>
I've never quite understood how that can be important (BTW, in the line from the "T" to outside, there's a check valve that will vent to cabin air in case some critter takes up residence in the end of the vent and stops it up.
Forgot to mention that ... Jim S.