the reason you soak bogwood is to wash out the tannines which stain your water brown, however the tannines don't actually harm your fish, and some species will in fact find it beneficial. so you don't ever have to soak bogwood. it's an optional thing based on your preference for the look of your tank. however when you are taking anything from someone elses tank what you have to think of is can you 100% guarantee that their tank is healthy, in very few cases can you answer yes to that. If there are any diseases then there is a chance of transferring them. so if it's possible i would boil the wood before putting it into my tank, if you can't then leave it to dry out for a good few days which should kill off any nasties then add it to your tank