My local yard will only buy propane tanks if they have the valves removed.
During the past year, I've prepped 15 tanks for scrap using this method: https://www.youtube.com/watch?v=ZO4zC7kn49s
It works well. I would suggest not using a tree that has any value to you as the straps can cut into the bark and damage it.
Also, I attach the top strap ratchet hooks over the flange on the top of the tank. I also fit a monkey wrench to the valve and slide a pipe over the wrench handle instead of using a pipe directly on the valve as shown in the video. This makes for a stronger grip.