Ok, I just discovered how to remove BtrFS from a bunch of drives. It got kind of hard at first but, thanks to the #btrfs channel, I discovered how.
for device in sd{d..g}; do dd if=/dev/zero of=/dev/$device bs=4k count=1 seek=16; done
This will remove a 4k block; starting from 64k. This did it.
Why would you like to do this? Well, just to try some different configurations. Also, I got into a problem while using different labels and stuff...