At the office, they have these electronic doors. On one of them in the bathroom, the cover for the batteries is broken off, so someone taped it back on with packing tape.

The doors are frosted glass. The packing tape’s adhesive fills in the microscopic pits of the frosting sufficiently and with a similar refractive index to glass, creating a “hole” in the glass.

Anyway, so packing tape lets you see into/out of the shitter.