Manyboats:
Yes, that installation was done by AT at the factory. Your are correct but I'm not sure there is anything I could do about it. The tanks are both symmetrical 90deg rectangular boxes mounted level on an enclosed portion of flooring out side the stringers. As for as I can determine, there is no "lowest corner". However, the two tanks (mounted starboard and port) are connected with a tee over the keel leading up to the engine. So to some extent, side to side motion of the boat could cause water in the bottom of the tank to spill over into that crossover and be trapped by the dual Raycor filters.