I don’t think I would use elecampane as an infusion herb. It has a very intense flavor and some of the constituents may be too strong for such a long steeping. I prefer tincture of the fresh herb or as a honey. I wrote a post about elecampane here:

It is a very powerful lung ally, specifically for eliminating respiratory infection. Another great one is mullein, which does make a very nice infusion using dried leaf, but strained through a cloth due to tiny hairs. I heat, mix with milk and honey. Mullein milk is yummy and helps irritated lungs.