After taking a brush and water hose to them, I spray mine down with that "Clorox Cleanup(a dilute bleach solution), let it sit for 5-10 minutes, then rinse them off under very hot water. I then spray them off with a vinegar solution and allow that to sit for about 10 minutes. Next, they are rinsed again, and I let them soak in clean hot water for 30 minutes and drain and rinse again. I might even let them sit in another tub of hot water again if I have the time. However, I don't put the rocks in the terrarium for at least 12 hours after that . . . just to let any bleach that MIGHT be left to dissipate.
Homer
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Homer W. Faucett III, esq.
Purveyor of All Trivialities