My favorite knot for a drawstring is a sliding type knot. Can't remember the name but it's like a prusik or hitch knot. It stays tight, but you can easily slide

My favorite knot for a drawstring is a sliding type knot. Can't remember the name but it's like a prusik or hitch knot. It stays tight, but you can easily slide it to tighten or loosen it, and you don't need to ever re-tie it.