If they have pieces in their tanks, see if they will sell you one. My LFS
does that all the time.
Other than that, unless you know what type of wood it is, you can't be sure about it being tank safe.
As for soaking, depending on the size, you can use a bucket, pot, plastic tub etc. I run all mine through the dishwasher, WITHOUT soap. The hot water helps penetrate the wood so it's easier to sink and it also cleans the wood.