This may be a bit too crazy sounding, but what it you added a float valve (like a toilet tank) to automatically turn off the air pressure when the water reached the proper level on the table? It could be as sinple as a valve, but if you modified a air pressure regulator to add an arm and a float, it would automatically fill the table and slowly turn itself off when the water was at the proper level. I've seen a few air pressure regulators used to automatically level optics tables and they have been modified with an arm to actuate the diaphragm in the regulator.
http://www.techmfg.com/products/adva...axdamp_lg.html http://www.techmfg.com/products/advanced/maxdamp.htm
Also, what about throwing in a few old magnets into the sump to help trap some of the magnetic slag? Perhaps a huge old ring magnet from a large subwoofer right around the drain sump? Or alternately, if most of the slag leftover is magnetic, you could put a PVC sink style sump (see pic) with magnets attached to the outside to catch the contaminants as they drain back to the tank, and the trap may catch the non-magnetic ones.
NEATman