I once made a contraption out of the top thread-part of a plastic soda bottle and the lid. Cut a slot down the threads, put your drawstring ends through the bottle end and slot, then tighten the cap to hold everything in place. plastic. survives the wash. Then my Dad suggested sewing the drawstring to the shorts at the midpoint with a few stitches. Much better, you don't have to make and remember to use any contraption.