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NachoConQueso
If the gunk was in your reservoir it is most likely still in your supply tubing. You probably won't be able to get it completely clean by just opening up the Blumats all the way because there will be a bottleneck from the 8 mm to 3 mm tubing. If you have a way to bleed the supply line at the end of the line that would be your best bet. Even if you have to do a partial disassembly it will probably be worth it to clear the line.
Between runs I like to run a weak bleach solution through all the tubing and then rinse with a bunch of water. I also use Drip Clean which is supposed to keep salts from building up in the lines but I don't think it would help with the gunk. Good luck.
I highly recommend using an on/off at the end of your supply line. You can open up the valve into a little container and you'd be surprised what comes out. I do it every res cleaning and my lines are always clean for the full run.