|I discovered this when I ruined a zipper while sewing on a waistband. After ripping out the now-useless zipper, I had no desire to go back and baste in the new one. So I re-basted the the zipper opening close. Then I applied Wash-Away Wonder Tape, which is about 1/8" wide, to the both edges of the zipper tape. I removed the paper backing and applied the zipper to the seam, centering the teeth over the seam. Once everything was in the right spot, I pressed down firmly over the tape. I then sewed in the zipper as usual. The tape is so narrow that it won't peek out if the center-slot happens to flap open. I like the end result so much that I will use this for all of my center-slot zippers. You can probably use the wonder-tape with a lapped zipper or maybe even a mock-fly.