Pant drawstring is the tape or ribbon that runs through a hem at the waist. When this ribbon or string is pulled, the opening is closed.
Hope this tutorial will help on a minor detail while stitching opening to thread through the rope to tie around the hip.
I used to be amazed when I see in ready made churidars or salwar, there will not be any long slit in the opening where we thread the rope. One fine day, I was so desperate and undid one of my old salwar bottom to get an idea.
Here, I will reproduce what I understood.
1. As usual fold 1/4th of an inch and stitch the raw edge on the top.
2. There will be two pieces of the belt / patti. On one side join the pieces fully at the breadth keeping the fabric right side facing the other right side. On the other side (that is at the opening), keep the right side facing the right side.
A. Stitch only for an inch, take out the needle from the fabric and pull the fabric away from you for an inch and then proceed joining till the end.
B. Now you will see an opening as in this picture. Now fold the raw edges like seen in the picture, then the fabric to right side.
3. Do top stitches on both sides, taking care to keep the opening as it is.
4. Now It will look like this
5. Fold one inch of the top edge towards wrong side, taking care to position the opening at the front.
6. Turn the fabric to the wrong side, stitch the folded edge making a tube to insert the tying rope through.
7. The final finish will be like this. I missed to take picture of the same fabric before giving it to client. So posting one of mine.
Compare both finishes and decide which one you want.