PfunMo, that's a helpful diagram. I'm not a structural engineer but since the OP wants to build the tank into the wall, isn't it safe to say that it is not a good idea to set it up within a load bearing wall? I would think that doing so could compromise the building's structural integrity. I was making this assumption in my post and my point was that if the tank is built into a wall that is perpendicular, but immediately adjacent, to a load bearing wall (or within a non-load bearing wall even further away from a load bearing wall), a lot of the weight of a four foot tank is going to be, at best, away from the supporting wall (as you move away from the wall the support provided by the load bearing wall is reduced) or at worst, not supported from below at all.
Perhaps I'm mistaken though in assuming you should not build a tank within a load bearing wall. :?