Like everyone else said. 91%+ Iso and Epsom Salt.
For Small Pieces I will pour Iso and Salt into a ziplock and shake around like there is no tomorrow. Always be sure to clear space around you so you do not slam you bag into something. Sounds dumb but you would be surprised
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I will shake for about 30 sec. then take out the piece, rinse and use cotton swabs dipped in Iso to scrape gunk off.
I usually do a few cycles of that before my piece is back to new. If gunk is extra heavy, blowing in the piece helps me,
(Always make sure the bowl is facing down!)
Good Luck!
And remember...the best way to keep a piece clean, is clean water. Always change water.