There are lots of opinions and techniques to use. First and foremost you need to have a good idea if your rivers are known for bad pollution. Once you find a good area and locate your piece look for soggy or rotting places on your dw. You want to avoid pieces with that on them. In the past I have used a wire brush to scrub the rotting places out of the wood. Once you find the piece you cant live with out you need to give it a good sniff. You do not want to smell the resins of pine, cedar or other types of wood. I have heard and read that certain species of wood can be a bad mix with your fish. Some people have gotten away with using it but I dont want to jeopardize my fish with a free piece of wood. Some say to avoid soft woods like the kind mentioned before because they will rot faster causing your water quality to suffer which is true but the dw was free so throw it out and go find another piece. Once I get my dw home I power wash it with my own power washer. I know mine has never had soaps or any other kind of chemical in it. After power washing I boil it for a couple hours and then I use it. It has been stated that boling wood breaks down the cellulose in the wood and causes it to break down faster(rot). Again...its free. I have also baked smaller pieces in my oven on the lowest setting. I believe temps between 140-160 will kill everything. These are pasteurizing temps. Now keep in mind this is my method. Some will pour boiling water over there dw and some will not do anything but scrub it off. So do as you wish and remember you are just trying to kill the bad stuff that lives on the wood, get the tannins out and or make it sink. Also try using the search function. There you can find all kinds of threads on the subject.