Cut the fabric in half so that you have two pieces measuring 30 inches by 36 inches.
Fold over an inch or so on each of the short ends of the fabric and sew making a channel for the drawstring.
With right sides together match up the sewn short ends and sew each side starting just below the stitching on the channels for each side. Be sure to backstitch a few times to secure the stitching.
Turn the bag right side out.
Cut enough drawstring to fit in the channel and a little extra. I used about 48 inches for each bag.
Wrap the frayed ends with tape just below the frayed part and cut.
Use a large safety pin and attach it to one end of the drawstring.
Thread the safety pin and string through the hole in the channel and all the way through the end. Continue into the next channel until you meet up with the beginning.
Add toggle cord stops to each end or thread both drawstrings through another stopper such as a tube or zip pull and then tie them together.