The peephole plug on my kiln falls out of the peephole during firing. How can I solve this problem?

You can wrap the peephole plug with a little ceramic fiber. That will hold the plug in place. Or you could also plug the peephole with ceramic fiber. If you have a downdraft kiln vent, it is important to keep the peepholes plugged during firing. Unplug them to view the witness cones on the shelf, then reinsert the plugs. If you don't have a downdraft vent, it is usually okay to leave the peephole plugs out altogether.