There are some kinds of wood you should stay away from, not sure which kinds though.But all Wood has sap, do you only mean fresh sap?
Somehow my reply to this the other day didn't post so I'm going to try and piece it back together. I feel the need for the wood to be really dried out (from previous sap etc) by nature and to be able to sink if possible are things that make finding the right stuff harder than what you describe. Over the years people have figured out what works and that's why you see certain types discussed so much if you do searches. Here's a good post:Is it just this easy, because nothing in Fish keeping is easy im probably wrong.
Find Wood Which Is not newly Cut so not green
Boil and clean it,
Soak For a week or two or untill it sinks.
Boil again.
Add to tank?
Tortea?