I actually have a similar problem. I only have ~250 gallons worth of aquariums, however my septic system is 60 years old and there is literally absolutely zero legal options to replace it (there are no places in my yard that are far enough away from pond / street / neighbor / well / house to be a legal distance by current law, and by a very wide margin it's not even close). So I'm paranoid about my septic on multiple levels (and no I don't know what will happen when it eventually fails, no I didn't know about this when I bought the house, yes my realtor was beyond incompetent).