A big tank of distilled or deionized water. Let it sit for a day, change the water, day, change, day change. Give it a good scrub with a non-static brush and cleaning mix of 10 parts water, 1 part isopropanol, and a bit of dish detergent. Then back into the water bath a couple of more times. Then a good rinse with pure isopropanol. Let it dry completely before powering it up.