but there are 2 metal bars that screw into the PSU and slide into clips on each hash board. Can anyone tell me what these bars are for?
I would prefer the PSU be outside the liquid and just mount the hash boards into the liquid, but how would I go about doing that with these bars attached?
Since the hashboards on T17 suck a lot of power, they had to use busbars instead of wires, of course also to improve the efficiency, your method will work as long as it's just a theory, but when applied in a real-world, it will probably fail, you see the output of that PSU is DC, and it outputs anywhere from 14.5 to 21 volts, DC connections are meant to stay as short as possible and it's hard to transmit, well the main reason why Edison lost the war of the currents 140 years ago.
If you measure the voltage on the furthest hashboard which is usually chain 2 ( in 0,1,2) you will see that it has slightly less voltage than the other two, by lengthening those busbars you will cause the voltage to drop even further, and since you want the miner to be inside a box and the PSU outside, then we are talking about a quite a bit of distance which could result in a very low voltage output which would indeed cause problems.
Now depending on how smart your design is, and say you won't add much distance, you might get away with it
I believe the manual says they are copper although they must be plates.
They are plated copper busbar, which is exactly what you have to use, you could use any plated copper bars you find but when you will have to tin/plate them after you make the wholes for the screws.
Honestly speaking, I would ditch the idea altogether, just throw the whole miner inside the liquid.
NotFuzzyWarm and HagssFIN would probably add more info and/or correct me if I made a mistake somewhere since they know about electcity much more than I do.