I have two 40's that I will possibly put in a Vector.  How big a tank is needed to get through the pattern with:

FP 40

B 40

B 40

B40 uses 3.5oz after it's broken in. It will take ~30-40 flights before fuel consumption drops to this level. My oldest running B40(started flying it in 2004) has been using 3.25oz for the past 3 seasons.

The recommended tank in the instructions is 4 oz.  I already bought one.  My guess is that the Brodak 40 does use a bit less fuel than the FP.  I was thinking about getting a smaller sized venturi for the FP.  I saw that idea here on another thread.  That apparently reduces fuel consumption but also power.  After reading some of these things I might be leaning toward the B-40.  I do think that the FP has more power.  I had the B-40 in a Smoothie that has gone the way of old planes.   

Depends. If its a box stock FP, then yes it does.
There's plenty of room in the nose of a Vector for a 4.5oz tank too.

Co-incidentally, both B40 and FP love APC 10.5x4.5!

I have put as much as a 5 ounce tank in a Vector. With a bit of this and that, it's possible to go to 5 1/2 ounces which is useful if you want to get a super sloppy rich run with an LA46. 4.5 is a good idea in your application. I have seen stock FP40s with marginal run times whne using a 4 ounce tank. Care especially needed to be taken when there was a chill in the air. I frequently used .273 venturis in stock FP40s. But this is with profiles like Twisters and Magicians. Fuel economy is better. Also takes the edge off the engine power. Suitable for planes that size. In Vectors, a considerably larger plane, usually heavier than a Twister or Magician, the smaller venturi (.283 is the large FP40 venturi size) might not provide enough power. Tho I have seen Vectors run successfully that way. I am told that Vector ARFs vary in weight. Earlier runs were lighter than the later runs. The FP40 with the smaller venturi (could have been a stock small venturi, a .265) was on an early Vector ARF. Flies very nicely.