on airsoft mechanics i have seen everything from soapy water to rubbing alcohol mentioned, a good number of people seem to use silicon to clean also.
But for legal reasons do not try this at home kids! Bad cheesman!Maybe less, you have to experiment for yourself. It depends on the size of the patch and the purity of your HCl. Drop it directly from the HCl into the NaOH, and then dry it off.
You can buy HCl granules, you would just mix them with water to mix up the liquid. Do some research into molarity and mixing solutions - this can go horribly wrong if you screw it up.