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            Marv,
        Regarding the two fuel vent options you mentioned;
        Running the vent back into the fuselage and up the seat back will trap     some fuel in the vent line at its lowest point.  The fuel system will     have to pull a bit of a vacuum to overcome pulling this trapped fuel     up hill out to the wing tip back into the tank.  Depending on the     diameter of the this line and given its length and the vibration it     will see, the line may never clear itself of fuel.  Unless the line is     very small in diameter, the vacuum created will start fuel on its way     out to the tip, the fluid column will break down flowing back to the     low point while allowing an air bubble to get past the fuel into the     tank, for the moment eliminating the vacuum.  If vibration were not     present the line would most likely clear itself, as soon as, fuel was     drawn from the tank.  Also, if the diameter is very small it will     clear itself.  Is this a bad situation?  Probably not, but I would     prefer using the vents to slightly positively pressurize the tanks     instead of potentially applying a small vacuum and forever trapping     fuel in the tubing.
        The concept of venting back to the tank could create a problem     depending on the details of the plumbing. If the vent line to the fuel     tank is submerged in fuel and the transfer pump is off, the engine     will create a vacuum inside the header tank.  Fuel will then be drawn     into the header tank, continuously, through either the fuel supply     line or vent, whichever offers the least resistance.  (This assumes     the wing tank is still vented otherwise everything locks up)  If you     route the header vent line to the highest point in the wing tank     everything works great until you get fuel in the vent line.  Now your     looking at the same situation as described in the first paragraph.          I have fuel out to the tips and find I rarely have to worry about     dumping fuel overboard.  With completely topped off tanks, turns on     the ground and uncoordinated flight will dump fuel, but that just     doesn't occur very often.  The vent line is as critical as the fuel     supply line in that, if it gets blocked, your fuel supply is useless.      I would suggest keeping it simple, inspectable and removable.          Chris Zavatson
    N91CZ