I soak them, but the peice I'm looking at now it super dead, so sap isn't really a problem. It's soaking right now actually.
I put the last peice in a running creek for a couple of months and then in a tub for two weeks, because it hadn't been dead as long. Still browned my water though. Don't have that luxury this time because it has been dry around here lately and the creek isn't flowing enough.