You're talking about the soil being moldy, or some bud? If it's bud, throw it out before you accidentally smoke it and kill yourself.

As for moldy soil -- dude, soil is cheap. It *might* be technically possible to flush it well enough and with the proper concoction to kill the mold (H202 works pretty well for this), but I don't know if I'd trust the soil after it's been through that. Just use fresh and don't worry.