If you don't want to deal with it see if you can find a local plating shop that will take used sollution of your hands. Waste treatement is actually more complex than the etching process. It needs to be neutralized to a PH of 9-10, and a coagulant added, ferric chloride is actually a very good for this, perhaps a little bit of clay. Not sure exactly how much but err on the side of 'just a little bit' After it's mixed at that PH For a few minutes let it sit for an hour, most of the metal and particulates in the solution should sink to the bottom. Drain off the clearer liquid on the top dilute with plenty of water (and actually only dumping it down the sewer drain right before a shower is a good idea) The rest should be used as the liquid part of a concrete mix and land filled at a hazardous waste facility. You can evaporate the leftovers down instead, but that's actually the bad stuff, just tossing that away is worse than dumping the raw solution down the drain.