The folks at Real Simple have a better idea. They swear by the potato method:
Start by grabbing a flashlight and turning off the lights in your kitchen. Shine the flashlight in the bottom of the dishwasher. Any pieces of glass will catch the light so you can see where they are. Then take 1/2 of a raw potato, and while wearing thick gloves, run the potato over the glass shards. The glass will become embedded in the potato and be easy to remove. Then simply run the washer on an empty cycle to rinse down any smaller pieces.
Read More: How To Remove Broken Glass From The Dishwasher from Real Simple