Got the sludge out! The fish tank IBC had been worrying me, as the pressure washer seemed to clean some parts, but they still felt slimy afterwards. Fortunately, some Simple Green + warm water + sponge and a plastic paint scraper together with some elbow grease produced a clean fish tank!
The growbed/sump that had glue in it I gave a once-over with the Simple Green as well, followed by some Comet… I figure if that is not enough, nothing reasonable will be. Worst case, I can exclude that GB/sump from the system. I’ll try putting some water in it and monitoring the pH change to see what happens.