I have always used the method of pinning a safety pin to the end of the drawstring that came out of sweat pants to feed it through the waistband until it comes out the other side to restring it. Here is another method that you may prefer: slide one end of the drawstring into a plastic straw. Secure with a piece of tape. Gently feed through the waistband inch by inch. The straw gives you control and length to slide smoothly through without bunching up. It’s a good idea to always tie hoodie or sweatpants drawstrings or secure the ends together with a safety pin before washing so you won’t have to go through this.