If you want to tan the beaver tail the scales will need to be removed first.What will remain then is the leather.Use regular agriculture barn lime.Same as liming a deer hide.Scales will scrape off after plumping up.
Delime it in borax or vinegar.
Use the bark tanning method to tan a bunch of them at once.I would'nt let them dry hard before tanning.After skinning and fleshing I would put them in the tanning liquor.
After they are tanned soften them with nets foot oil by massaging/scuffing them.
You can dye it any color you want after you are finished.