You should ask 4Metals to look at your design, or maybe one of the engineers on this forum. They might be missing this post all together because of the threads title.
it seems to me that if you are forcing air down a bypass to pick up air from your fume hood, then forcing it into a water tank that you would have to be drawing at least as many CFM at the T of your eductor to insure you didn't over pressurize your system. The problem is that you are forcing air into one end of your system, and sucking at the other end. If you try to ram too much air into the first part of your system then your pre-tank will become pressurized and will no longer accept the airflow which would cause a back feed of fumes back into your enclosure.
Anything that didn't get neutralized in the tank will go out with the water, and there is no guarantee that one pass through one tank will neutralize the fumes correctly, also what type of media are you planning to do the neutralization?
The idea is to keep the fumes in contact with the water, for a long enough period of time so that the water can absorb the acid fumes. At some point you either need to have the fumes in contact with the water for a longer period of time, or you need to circulate them so that they stay in contact with water for a longer period of time. To me, and this is only my opinion because I am not engineer, but it seems like the gas you are forcing into the first tank will quickly build up pressure and bleed back into your fume hood or leak out somewhere else. What little gas comes into contact with your water will eventually be sucked if you have a strong enough eductor, but still will not be in contact with water long enough to ensure they gas is absorbed by the water, but then you are expelling the water, and I feel that since the gas was not fully absorbed into the water in the first tank, even if it has the media to neutralize the acid in the water, it is not effective because as soon as the gas makes it's way to the surface of the water, it is already making it's way to the eductor to be sent down the drain.
Also, your system is dependent upon a constant water supply.
It just seems to me, and i could be wrong, that you would be sending acidic water down the drain.
I hope someone corrects me if I am wrong about this, to me it seems very likely, and I think I'm correct in this assumption, but I also want to make sure that what I believe is true will not lead anyone in the wrong direction.
