try to get green wood.
Strip the bark off to remove most of the critters and any pollution. Scrub them and wash well with a hose pipe. Then leave them for a while to let the wood dry out properly. It takes a couple of weeks+ for the sap to dry out IME.
You can put them in the microwave, bleach them, cook them, pour boiling water over them freeze them. It'll make them a bit cleaner and a bit more sterile bit it's probably unnecessary. I just start using them and haven't had a problem.
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